diff --git a/book/src/applet/prelude/store.rs b/book/src/applet/prelude/store.rs
index e20f4708..5c918a04 100644
--- a/book/src/applet/prelude/store.rs
+++ b/book/src/applet/prelude/store.rs
@@ -96,7 +96,7 @@ impl<'a> Command<'a> {
     //} ANCHOR_END: impl_parse
 
     //{ ANCHOR: process_signature
-    fn process(&self) -> Result<(), store::Error> {
+    fn process(&self) -> Result<(), Error> {
         //} ANCHOR_END: process_signature
         //{ ANCHOR: process_insert
         match self {
@@ -160,21 +160,21 @@ impl Key {
 }
 
 //{ ANCHOR: helpers
-fn insert(key: &Key, value: &[u8]) -> Result<(), store::Error> {
+fn insert(key: &Key, value: &[u8]) -> Result<(), Error> {
     match key {
         Key::Exact(key) => store::insert(*key, value),
         Key::Range(keys) => store::fragment::insert(keys.clone(), value),
     }
 }
 
-fn find(key: &Key) -> Result<Option<Box<[u8]>>, store::Error> {
+fn find(key: &Key) -> Result<Option<Box<[u8]>>, Error> {
     match key {
         Key::Exact(key) => store::find(*key),
         Key::Range(keys) => store::fragment::find(keys.clone()),
     }
 }
 
-fn remove(key: &Key) -> Result<(), store::Error> {
+fn remove(key: &Key) -> Result<(), Error> {
     match key {
         Key::Exact(key) => store::remove(*key),
         Key::Range(keys) => store::fragment::remove(keys.clone()),
diff --git a/crates/api-desc/CHANGELOG.md b/crates/api-desc/CHANGELOG.md
index 14e14810..79249658 100644
--- a/crates/api-desc/CHANGELOG.md
+++ b/crates/api-desc/CHANGELOG.md
@@ -4,6 +4,8 @@
 
 ### Minor
 
+- Remove isize conversion functions for enums
+- Remove custom error types
 - Add `gpio` module
 - Add `platform::version()`
 - Add `radio::ble` module
diff --git a/crates/api-desc/src/crypto.rs b/crates/api-desc/src/crypto.rs
index 1c12b0f2..34004255 100644
--- a/crates/api-desc/src/crypto.rs
+++ b/crates/api-desc/src/crypto.rs
@@ -24,24 +24,6 @@ pub(crate) fn new() -> Item {
         /// Cryptographic operations.
     };
     let name = "crypto".into();
-    let items = vec![
-        item! {
-            /// Describes errors on cryptographic operations.
-            enum Error {
-                /// A function pre-condition was broken.
-                InvalidArgument = 0,
-
-                /// An operation is unsupported.
-                Unsupported = 1,
-
-                /// An RNG operation failed.
-                RngFailure = 2,
-            }
-        },
-        ccm::new(),
-        ec::new(),
-        gcm::new(),
-        hash::new(),
-    ];
+    let items = vec![ccm::new(), ec::new(), gcm::new(), hash::new()];
     Item::Mod(Mod { docs, name, items })
 }
diff --git a/crates/api-desc/src/crypto/ccm.rs b/crates/api-desc/src/crypto/ccm.rs
index d1cff300..48117df2 100644
--- a/crates/api-desc/src/crypto/ccm.rs
+++ b/crates/api-desc/src/crypto/ccm.rs
@@ -53,8 +53,7 @@ pub(crate) fn new() -> Item {
                 /// Its length must be `len + 4` bytes.
                 cipher: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
@@ -83,8 +82,7 @@ pub(crate) fn new() -> Item {
                 /// Its length must be provided in the `len` field.
                 clear: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
diff --git a/crates/api-desc/src/crypto/ec.rs b/crates/api-desc/src/crypto/ec.rs
index 6fd58c34..f08a1f81 100644
--- a/crates/api-desc/src/crypto/ec.rs
+++ b/crates/api-desc/src/crypto/ec.rs
@@ -82,8 +82,7 @@ pub(crate) fn new() -> Item {
                 /// The y coordinate in SEC1 encoding.
                 y: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
@@ -108,8 +107,7 @@ pub(crate) fn new() -> Item {
                 /// The y coordinate of the output point in SEC1 encoding.
                 out_y: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
@@ -131,8 +129,7 @@ pub(crate) fn new() -> Item {
                 /// The s signature component in SEC1 encoding.
                 s: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
@@ -157,8 +154,7 @@ pub(crate) fn new() -> Item {
                 /// The s signature component in SEC1 encoding.
                 s: *const u8,
             } -> {
-                /// 1 if the signature is valid, 0 if invalid, and bitwise complement of
-                /// [`Error`](crate::crypto::Error) otherwise.
+                /// One if the signature is valid. Zero if invalid. Negative on error.
                 res: isize,
             }
         },
diff --git a/crates/api-desc/src/crypto/gcm.rs b/crates/api-desc/src/crypto/gcm.rs
index 64098e8a..14dd169c 100644
--- a/crates/api-desc/src/crypto/gcm.rs
+++ b/crates/api-desc/src/crypto/gcm.rs
@@ -78,8 +78,7 @@ pub(crate) fn new() -> Item {
                 /// The authentication tag (see [`super::tag_length()`]).
                 tag: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
@@ -113,8 +112,7 @@ pub(crate) fn new() -> Item {
                 /// The clear text.
                 clear: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
diff --git a/crates/api-desc/src/crypto/hash.rs b/crates/api-desc/src/crypto/hash.rs
index 177bb941..1558a170 100644
--- a/crates/api-desc/src/crypto/hash.rs
+++ b/crates/api-desc/src/crypto/hash.rs
@@ -46,8 +46,7 @@ pub(crate) fn new() -> Item {
                 /// The hash algorithm.
                 algorithm: usize,
             } -> {
-                /// A non-negative identifier on success, bitwise complement of
-                /// [`Error`](crate::crypto::Error) otherwise.
+                /// Negative on error. The identifier otherwise.
                 id: isize,
             }
         },
@@ -83,8 +82,7 @@ pub(crate) fn new() -> Item {
                 /// without computing the digest.
                 digest: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
@@ -112,8 +110,7 @@ pub(crate) fn new() -> Item {
                 /// If greater than 64 bytes, the key will be itself hashed.
                 key_len: usize,
             } -> {
-                /// A non-negative identifier on success, bitwise complement of
-                /// [`Error`](crate::crypto::Error) otherwise.
+                /// Negative on error. The identifier otherwise.
                 id: isize,
             }
         },
@@ -149,8 +146,7 @@ pub(crate) fn new() -> Item {
                 /// without computing the hmac.
                 hmac: *mut u8,
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative otherwise.
                 res: isize,
             }
         },
@@ -197,8 +193,7 @@ pub(crate) fn new() -> Item {
                 okm_len: usize,
 
             } -> {
-                /// Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-                /// otherwise.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
diff --git a/crates/api-desc/src/lib.rs b/crates/api-desc/src/lib.rs
index e14599fc..5b5a67c6 100644
--- a/crates/api-desc/src/lib.rs
+++ b/crates/api-desc/src/lib.rs
@@ -205,9 +205,6 @@ impl Enum {
             impl From<#name> for crate::U32<usize> {
                 fn from(x: #name) -> Self { (x as u32).into() }
             }
-            impl From<#name> for crate::U32<isize> {
-                fn from(x: #name) -> Self { (!(x as u32)).into() }
-            }
         }
     }
 
@@ -221,12 +218,6 @@ impl Enum {
                     (x as u32).try_into().unwrap()
                 }
             }
-            impl #name {
-                pub fn to_result(x: isize) -> Result<usize, Self> {
-                    let y = x as usize;
-                    if x < 0 { Err((!y).into()) } else { Ok(y) }
-                }
-            }
         }
     }
 
@@ -241,20 +232,17 @@ impl Enum {
             #[repr(u32)]
             pub enum #name { #(#variants),* }
             impl TryFrom<u32> for #name {
-                type Error = ();
+                type Error = wasefire_error::Error;
 
                 fn try_from(x: u32) -> Result<Self, Self::Error> {
                     if x < #num_variants as u32 {
                         // SAFETY: See `tests::enum_values_are_valid()`.
                         Ok(unsafe { core::mem::transmute(x) })
                     } else {
-                        Err(())
+                        Err(wasefire_error::Error::internal(0))
                     }
                 }
             }
-            impl From<#name> for isize {
-                fn from(x: #name) -> Self { !(x as usize) as isize }
-            }
         }
     }
 
diff --git a/crates/api-desc/src/radio.rs b/crates/api-desc/src/radio.rs
index e51618eb..ff5e6f59 100644
--- a/crates/api-desc/src/radio.rs
+++ b/crates/api-desc/src/radio.rs
@@ -21,14 +21,6 @@ pub(crate) fn new() -> Item {
         /// Radio operations.
     };
     let name = "radio".into();
-    let items = vec![
-        item! {
-            /// Describes errors on radio operations.
-            enum Error {
-                Unknown = 0,
-            }
-        },
-        ble::new(),
-    ];
+    let items = vec![ble::new()];
     Item::Mod(Mod { docs, name, items })
 }
diff --git a/crates/api-desc/src/radio/ble.rs b/crates/api-desc/src/radio/ble.rs
index bb0a20a1..894cb9a3 100644
--- a/crates/api-desc/src/radio/ble.rs
+++ b/crates/api-desc/src/radio/ble.rs
@@ -46,8 +46,8 @@ pub(crate) fn new() -> Item {
                 /// Pointer to the [`super::Advertisement`] packet.
                 ptr: *mut u8,
             } -> {
-                /// One if a packet was read. Zero if there was no packet to read. Otherwise
-                /// complement of error number.
+                /// One if a packet was read. Zero if there was no packet to read. Negative on
+                /// error.
                 res: isize,
             }
         },
diff --git a/crates/api-desc/src/store.rs b/crates/api-desc/src/store.rs
index ab3536f8..eb81cfe0 100644
--- a/crates/api-desc/src/store.rs
+++ b/crates/api-desc/src/store.rs
@@ -22,25 +22,6 @@ pub(crate) fn new() -> Item {
     };
     let name = "store".into();
     let items = vec![
-        item! {
-            /// Describes errors interacting with the store.
-            enum Error {
-                /// A function pre-condition was broken.
-                InvalidArgument = 0,
-
-                /// The store is full.
-                NoCapacity = 1,
-
-                /// The store reached its end of life.
-                NoLifetime = 2,
-
-                /// An operation to the underlying storage failed.
-                StorageError = 3,
-
-                /// The underlying storage doesn't match the store invariant.
-                InvalidStorage = 4,
-            }
-        },
         item! {
             /// Inserts an entry in the store.
             ///
@@ -57,7 +38,7 @@ pub(crate) fn new() -> Item {
                 /// Length of the value.
                 len: usize,
             } -> {
-                /// Zero for success. Otherwise complement of error number.
+                /// Zero for success. Negative on error.
                 res: isize,
             }
         },
@@ -69,7 +50,7 @@ pub(crate) fn new() -> Item {
                 /// Key of the entry.
                 key: usize,
             } -> {
-                /// Zero for success. Otherwise complement of error number.
+                /// Zero for success. Negative on error.
                 res: isize,
             }
         },
@@ -97,11 +78,11 @@ pub(crate) fn new() -> Item {
                 #[cfg(feature = "multivalue")]
                 ptr: *mut u8,
 
-                /// Length of the value if non-negative. Otherwise complement of error number.
+                /// Negative on error. Otherwise length of the value.
                 #[cfg(feature = "multivalue")]
                 len: isize,
 
-                /// One if found. Zero if not found. Otherwise complement of error number.
+                /// One if found. Zero if not found. Negative on error.
                 #[cfg(not(feature = "multivalue"))]
                 res: isize,
             }
diff --git a/crates/api-desc/src/usb.rs b/crates/api-desc/src/usb.rs
index 0f22d856..231f50e8 100644
--- a/crates/api-desc/src/usb.rs
+++ b/crates/api-desc/src/usb.rs
@@ -21,14 +21,6 @@ pub(crate) fn new() -> Item {
         /// USB operations.
     };
     let name = "usb".into();
-    let items = vec![
-        item! {
-            /// Describes errors on USB operations.
-            enum Error {
-                Unknown = 0,
-            }
-        },
-        serial::new(),
-    ];
+    let items = vec![serial::new()];
     Item::Mod(Mod { docs, name, items })
 }
diff --git a/crates/api-desc/src/usb/serial.rs b/crates/api-desc/src/usb/serial.rs
index af594928..c2f9c357 100644
--- a/crates/api-desc/src/usb/serial.rs
+++ b/crates/api-desc/src/usb/serial.rs
@@ -76,7 +76,7 @@ pub(crate) fn new() -> Item {
         item! {
             /// Flushs the USB serial.
             fn flush "usf" {} -> {
-                /// Zero on success, -1 on error.
+                /// Zero on success. Negative on error.
                 res: isize,
             }
         },
diff --git a/crates/api/CHANGELOG.md b/crates/api/CHANGELOG.md
index 1cda05dc..0ada0175 100644
--- a/crates/api/CHANGELOG.md
+++ b/crates/api/CHANGELOG.md
@@ -6,6 +6,10 @@
 
 - Update `wasefire-applet-api-macro` version
 
+### Minor
+
+- Implement conversion from types involving `Error` to `U32`
+
 ### Patch
 
 - Build docs.rs for `wasm32-unknown-unknown` only
@@ -68,4 +72,4 @@
 
 ## 0.1.0
 
-<!-- Increment to skip CHANGELOG.md test: 6 -->
+<!-- Increment to skip CHANGELOG.md test: 7 -->
diff --git a/crates/api/Cargo.lock b/crates/api/Cargo.lock
index cd270166..eadbd85e 100644
--- a/crates/api/Cargo.lock
+++ b/crates/api/Cargo.lock
@@ -104,6 +104,26 @@ version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "95505c38b4572b2d910cecb0281560f54b440a19336cbbcb27bf6ce6adc6f5a8"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.70"
@@ -169,6 +189,7 @@ dependencies = [
  "bytemuck",
  "sealed",
  "wasefire-applet-api-macro",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
@@ -193,6 +214,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-logger"
 version = "0.1.4-git"
diff --git a/crates/api/Cargo.toml b/crates/api/Cargo.toml
index ce33c6dd..b494b13d 100644
--- a/crates/api/Cargo.toml
+++ b/crates/api/Cargo.toml
@@ -19,6 +19,7 @@ features = ["wasm"]
 bytemuck = { version = "1.14.0", default-features = false, features = ["derive"] }
 sealed = { version = "0.5.0", default-features = false, optional = true }
 wasefire-applet-api-macro = { version = "0.6.0-git", path = "../api-macro" }
+wasefire-error = { version = "0.1.0-git", path = "../error" }
 wasefire-logger = { version = "0.1.4-git", path = "../logger", optional = true }
 
 [features]
diff --git a/crates/api/src/host.rs b/crates/api/src/host.rs
index 108e1d4f..ccc436d2 100644
--- a/crates/api/src/host.rs
+++ b/crates/api/src/host.rs
@@ -17,6 +17,7 @@ use core::marker::PhantomData;
 use core::ops::Deref;
 
 use sealed::sealed;
+use wasefire_error::Error;
 
 /// Describes an interface function at type-level.
 #[sealed(pub(crate))]
@@ -81,6 +82,30 @@ impl<T> From<u32> for U32<T> {
     }
 }
 
+impl<T> From<Error> for U32<T> {
+    fn from(error: Error) -> Self {
+        (Error::encode(Err(error)) as u32).into()
+    }
+}
+
+impl<T> From<Result<(), Error>> for U32<T> {
+    fn from(result: Result<(), Error>) -> Self {
+        result.map(|()| 0).into()
+    }
+}
+
+impl<T> From<Result<bool, Error>> for U32<T> {
+    fn from(result: Result<bool, Error>) -> Self {
+        result.map(|x| x as u32).into()
+    }
+}
+
+impl<T> From<Result<u32, Error>> for U32<T> {
+    fn from(result: Result<u32, Error>) -> Self {
+        (Error::encode(result) as u32).into()
+    }
+}
+
 #[sealed(pub(crate))]
 pub trait ArrayU32: Sized + Copy {
     const LENGTH: usize = core::mem::size_of::<Self>() / core::mem::size_of::<u32>();
diff --git a/crates/board/CHANGELOG.md b/crates/board/CHANGELOG.md
index f55b70eb..358d1ef1 100644
--- a/crates/board/CHANGELOG.md
+++ b/crates/board/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Major
 
+- Replace `Error` type with `wasefire-error`
 - Add `Api::Gpio` for low-level GPIOs
 - Add `platform::Api::version()`
 - Add `Api::Radio` for radio APIs
diff --git a/crates/board/Cargo.lock b/crates/board/Cargo.lock
index fc0bc665..9ca619f8 100644
--- a/crates/board/Cargo.lock
+++ b/crates/board/Cargo.lock
@@ -492,7 +492,16 @@ version = "0.6.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7a015b430d3c108a207fd776d2e2196aaf8b1cf8cf93253e3a097ff3085076a1"
 dependencies = [
- "num_enum_derive",
+ "num_enum_derive 0.6.1",
+]
+
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive 0.7.1",
 ]
 
 [[package]]
@@ -506,6 +515,17 @@ dependencies = [
  "syn 2.0.41",
 ]
 
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "opaque-debug"
 version = "0.3.0"
@@ -780,7 +800,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e73e438f527e567fb3982f2370967821fab4f5aea84c42e218a211dd2002b6a2"
 dependencies = [
  "heapless",
- "num_enum",
+ "num_enum 0.6.1",
  "portable-atomic",
 ]
 
@@ -814,6 +834,7 @@ dependencies = [
  "bytemuck",
  "sealed",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -862,10 +883,18 @@ dependencies = [
  "usb-device",
  "usbd-serial",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-logger",
  "wasefire-store",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum 0.7.1",
+]
+
 [[package]]
 name = "wasefire-logger"
 version = "0.1.4-git"
diff --git a/crates/board/Cargo.toml b/crates/board/Cargo.toml
index cedb2d5f..9bb3eeb7 100644
--- a/crates/board/Cargo.toml
+++ b/crates/board/Cargo.toml
@@ -36,6 +36,7 @@ typenum = { version = "1.17.0", default-features = false }
 usb-device = { version = "0.3.1", default-features = false }
 usbd-serial = { version = "0.2.0", default-features = false }
 wasefire-applet-api = { version = "0.6.0-git", path = "../api", features = ["host"] }
+wasefire-error = { version = "0.1.0-git", path = "../error" }
 wasefire-logger = { version = "0.1.4-git", path = "../logger" }
 wasefire-store = { version = "0.2.3-git", path = "../store" }
 
diff --git a/crates/board/src/crypto/aead.rs b/crates/board/src/crypto/aead.rs
index cf1531cb..6683a115 100644
--- a/crates/board/src/crypto/aead.rs
+++ b/crates/board/src/crypto/aead.rs
@@ -121,7 +121,7 @@ mod software {
                 cipher.copy_from_slice(clear);
             }
             tag.copy_from_slice(
-                &aead.encrypt_in_place_detached(iv, aad, cipher).map_err(|_| Error::World)?,
+                &aead.encrypt_in_place_detached(iv, aad, cipher).map_err(|_| Error::world(0))?,
             );
             Ok(())
         }
@@ -134,7 +134,7 @@ mod software {
             if let Some(cipher) = cipher {
                 clear.copy_from_slice(cipher);
             }
-            aead.decrypt_in_place_detached(iv, aad, clear, tag).map_err(|_| Error::World)
+            aead.decrypt_in_place_detached(iv, aad, clear, tag).map_err(|_| Error::world(0))
         }
     }
 }
diff --git a/crates/board/src/crypto/ecc.rs b/crates/board/src/crypto/ecc.rs
index fc6236bd..48f1da0f 100644
--- a/crates/board/src/crypto/ecc.rs
+++ b/crates/board/src/crypto/ecc.rs
@@ -142,7 +142,7 @@ mod software {
         fn ecdsa_sign(d: &Int<C>, m: &Int<C>, r: &mut Int<C>, s: &mut Int<C>) -> Result<(), Error> {
             let d = Self::scalar_from_int(d)?;
             let (signature, _) =
-                d.try_sign_prehashed_rfc6979::<D>(m, &[]).map_err(|_| Error::World)?;
+                d.try_sign_prehashed_rfc6979::<D>(m, &[]).map_err(|_| Error::world(0))?;
             r.copy_from_slice(&Self::scalar_to_int(signature.r()));
             s.copy_from_slice(&Self::scalar_to_int(signature.s()));
             Ok(())
@@ -152,9 +152,9 @@ mod software {
             m: &Int<C>, x: &Int<C>, y: &Int<C>, r: &Int<C>, s: &Int<C>,
         ) -> Result<bool, Error> {
             let p = EncodedPoint::<C>::from_affine_coordinates(x, y, false);
-            let p = VerifyingKey::<C>::from_encoded_point(&p).map_err(|_| Error::User)?;
+            let p = VerifyingKey::<C>::from_encoded_point(&p).map_err(|_| Error::user(0))?;
             let signature =
-                Signature::from_scalars(r.clone(), s.clone()).map_err(|_| Error::User)?;
+                Signature::from_scalars(r.clone(), s.clone()).map_err(|_| Error::user(0))?;
             Ok(p.verify_prehash(m, &signature).is_ok())
         }
     }
@@ -181,13 +181,13 @@ mod software {
 
         fn point_to_ints(p: &AffinePoint<C>, x: &mut Int<C>, y: &mut Int<C>) -> Result<(), Error> {
             let p = p.to_encoded_point(false);
-            x.copy_from_slice(p.x().ok_or(Error::User)?);
-            y.copy_from_slice(p.y().ok_or(Error::User)?);
+            x.copy_from_slice(p.x().ok_or(Error::user(0))?);
+            y.copy_from_slice(p.y().ok_or(Error::user(0))?);
             Ok(())
         }
     }
 
     fn convert<T>(x: CtOption<T>) -> Result<T, Error> {
-        Option::<T>::from(x).ok_or(Error::User)
+        Option::<T>::from(x).ok_or(Error::user(0))
     }
 }
diff --git a/crates/board/src/lib.rs b/crates/board/src/lib.rs
index 5bb6ff0d..dc6c24f4 100644
--- a/crates/board/src/lib.rs
+++ b/crates/board/src/lib.rs
@@ -26,6 +26,7 @@ use core::marker::PhantomData;
 use core::ops::Deref;
 
 use derivative::Derivative;
+pub use wasefire_error::Error;
 
 pub mod button;
 pub mod crypto;
@@ -124,21 +125,6 @@ pub enum Event<B: Api + ?Sized> {
     Usb(usb::Event),
 }
 
-/// Errors that interfaces may return.
-///
-/// Because a board interfaces between the user and the world, there's 2 types of errors: those due
-/// to the user and those due to the world. If the board itself errors, the error should be handled
-/// internally: either by an automatic reset (in production) or by halting execution until a manual
-/// reset (during testing to permit debugging).
-#[derive(Debug, Copy, Clone)]
-pub enum Error {
-    /// The user made an error.
-    User,
-
-    /// The world made an error.
-    World,
-}
-
 pub type Button<B> = <B as Api>::Button;
 pub type Crypto<B> = <B as Api>::Crypto;
 pub type Debug<B> = <B as Api>::Debug;
diff --git a/crates/board/src/platform.rs b/crates/board/src/platform.rs
index c79c7345..db762c79 100644
--- a/crates/board/src/platform.rs
+++ b/crates/board/src/platform.rs
@@ -14,6 +14,8 @@
 
 //! Platform interface.
 
+use wasefire_error::Code;
+
 use crate::{Error, Unsupported};
 
 pub mod update;
@@ -44,6 +46,6 @@ impl Api for Unsupported {
     }
 
     fn reboot() -> Result<!, Error> {
-        Err(Error::World)
+        Err(Error::internal(Code::NotImplemented))
     }
 }
diff --git a/crates/board/src/rng.rs b/crates/board/src/rng.rs
index 6924bd8b..81a0929c 100644
--- a/crates/board/src/rng.rs
+++ b/crates/board/src/rng.rs
@@ -14,6 +14,8 @@
 
 //! Random number generator interface.
 
+use wasefire_error::Code;
+
 use crate::{Error, Unsupported};
 
 /// Random number generator interface.
@@ -24,6 +26,6 @@ pub trait Api: Send {
 
 impl Api for Unsupported {
     fn fill_bytes(_: &mut [u8]) -> Result<(), Error> {
-        Err(Error::World)
+        Err(Error::internal(Code::NotImplemented))
     }
 }
diff --git a/crates/board/src/usb/serial.rs b/crates/board/src/usb/serial.rs
index b66e0afa..7da9db12 100644
--- a/crates/board/src/usb/serial.rs
+++ b/crates/board/src/usb/serial.rs
@@ -138,7 +138,7 @@ impl<T: HasSerial> Api for WithSerial<T> {
             Err(UsbError::WouldBlock) => Ok(0),
             Err(e) => {
                 log::debug!("{} = read({})", log::Debug2Format(&e), output.len());
-                Err(Error::World)
+                Err(Error::world(0))
             }
         }
     }
@@ -156,7 +156,7 @@ impl<T: HasSerial> Api for WithSerial<T> {
             Err(UsbError::WouldBlock) => Ok(0),
             Err(e) => {
                 log::debug!("{} = write({}{:?})", log::Debug2Format(&e), input.len(), input);
-                Err(Error::World)
+                Err(Error::world(0))
             }
         }
     }
@@ -174,7 +174,7 @@ impl<T: HasSerial> Api for WithSerial<T> {
                 }
                 Err(e) => {
                     log::debug!("{} = flush()", log::Debug2Format(&e));
-                    break Err(Error::World);
+                    break Err(Error::world(0));
                 }
             }
         }
diff --git a/crates/error/CHANGELOG.md b/crates/error/CHANGELOG.md
new file mode 100644
index 00000000..7bcc0814
--- /dev/null
+++ b/crates/error/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Changelog
+
+## 0.1.0-git
+
+<!-- Increment to skip CHANGELOG.md test: 1 -->
diff --git a/crates/error/Cargo.lock b/crates/error/Cargo.lock
new file mode 100644
index 00000000..0898d4ee
--- /dev/null
+++ b/crates/error/Cargo.lock
@@ -0,0 +1,65 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.70"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39278fbbf5fb4f646ce651690877f89d1c5811a3d4acb27700c1cb3cdb78fd3b"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.33"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5267fca4496028628a95160fc423a33e8b2e6af8a5302579e322e4b520293cae"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.41"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44c8b28c477cc3bf0e7966561e3460130e1255f7a1cf71931075f1c5e7a7e269"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b"
+
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
diff --git a/crates/error/Cargo.toml b/crates/error/Cargo.toml
new file mode 100644
index 00000000..7e4f9d06
--- /dev/null
+++ b/crates/error/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "wasefire-error"
+version = "0.1.0-git"
+authors = ["Julien Cretin <cretin@google.com>"]
+license = "Apache-2.0"
+publish = true
+edition = "2021"
+description = "Wasefire API errors"
+repository = "https://github.com/google/wasefire"
+include = ["/src"]
+keywords = ["embedded", "framework", "no-std"]
+categories = ["embedded", "no-std"]
+
+[dependencies]
+num_enum = { version = "0.7.1", default-features = false }
diff --git a/crates/error/src/lib.rs b/crates/error/src/lib.rs
new file mode 100644
index 00000000..4136890f
--- /dev/null
+++ b/crates/error/src/lib.rs
@@ -0,0 +1,171 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Applet and board API errors.
+
+#![no_std]
+
+use num_enum::{IntoPrimitive, TryFromPrimitive, TryFromPrimitiveError};
+
+/// API errors.
+///
+/// Errors are equivalent to `u32` but only using the 24 least significant bits: 8 bits for the
+/// error space and 16 bits for the error code. The 8 most significant bits are zero. It is possible
+/// to encode a `Result<u32, Error>` into a `i32` as long as the success value only uses the 31
+/// least significant bits. Non-negative values encode success, while negative values encode the
+/// error by taking its bitwise complement (thus setting the 8 most significant bits to 1).
+#[derive(Default, Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
+#[repr(transparent)]
+pub struct Error(u32);
+
+impl Error {
+    /// Creates a new error.
+    pub fn new(space: impl SpaceParam, code: impl CodeParam) -> Self {
+        Error((space.into() as u32) << 16 | code.into() as u32)
+    }
+
+    /// Returns the error space.
+    pub fn space(self) -> u8 {
+        (self.0 >> 16) as u8
+    }
+
+    /// Returns the error code.
+    pub fn code(self) -> u16 {
+        self.0 as u16
+    }
+
+    /// Creates a user error.
+    pub fn user(code: impl CodeParam) -> Self {
+        Error::new(Space::User, code)
+    }
+
+    /// Creates an internal error.
+    pub fn internal(code: impl CodeParam) -> Self {
+        Error::new(Space::Internal, code)
+    }
+
+    /// Creates a world error.
+    pub fn world(code: impl CodeParam) -> Self {
+        Error::new(Space::World, code)
+    }
+
+    /// Decodes a signed integer as a result (where errors are negative values).
+    ///
+    /// # Panics
+    ///
+    /// Panics if the signed integer is smaller than -16777216 (0xff000000).
+    pub fn decode(result: i32) -> Result<u32, Self> {
+        if result < 0 {
+            let error = !result as u32;
+            assert!(error & 0xff000000 == 0);
+            Err(Error(error))
+        } else {
+            Ok(result as u32)
+        }
+    }
+
+    /// Encodes a result (where errors are negative values) as a signed integer.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the result is a success greater than 2147483647 (0x7fffffff).
+    pub fn encode(result: Result<u32, Self>) -> i32 {
+        match result {
+            Ok(value) => {
+                let value = value as i32;
+                assert!(0 <= value);
+                value
+            }
+            Err(Error(error)) => !error as i32,
+        }
+    }
+}
+
+pub trait SpaceParam: Into<u8> {}
+impl SpaceParam for Space {}
+impl SpaceParam for u8 {}
+
+pub trait CodeParam: Into<u16> {}
+impl CodeParam for Code {}
+impl CodeParam for u16 {}
+
+/// Common error spaces.
+///
+/// Values from 0 to 127 (0x7f) are reserved for common error spaces and defined by this enum.
+/// Values from 128 (0x80) to 255 (0xff) are reserved for implementation-specific error spaces.
+#[derive(Debug, Copy, Clone, TryFromPrimitive, IntoPrimitive)]
+#[non_exhaustive]
+#[repr(u8)]
+pub enum Space {
+    Generic = 0,
+
+    /// The user made an error.
+    User = 1,
+
+    /// The implementation failed.
+    Internal = 2,
+
+    /// The world returned an error.
+    World = 3,
+}
+
+/// Common error codes.
+///
+/// Values from 0 to 32767 (0x7fff) are reserved for common error codes and defined by this enum.
+/// Values from 32768 (0x8000) to 65535 (0xffff) are reserved for implementation-specific error
+/// codes.
+#[derive(Debug, Copy, Clone, TryFromPrimitive, IntoPrimitive)]
+#[non_exhaustive]
+#[repr(u16)]
+pub enum Code {
+    Generic = 0,
+    NotImplemented = 1,
+    NotFound = 2,
+    BadSize = 3,
+    BadAlign = 4,
+    NoPermission = 5,
+    NotEnough = 6,
+    BadState = 7,
+}
+
+impl core::fmt::Display for Error {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match Space::try_from_primitive(self.space()) {
+            Ok(x) => write!(f, "{x:?}")?,
+            Err(TryFromPrimitiveError { number: x }) => write!(f, "[{x:02x}]")?,
+        }
+        write!(f, ":")?;
+        match Code::try_from_primitive(self.code()) {
+            Ok(x) => write!(f, "{x:?}"),
+            Err(TryFromPrimitiveError { number: x }) => write!(f, "[{x:04x}]"),
+        }
+    }
+}
+
+impl core::fmt::Debug for Error {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "{self}")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn new_ok() {
+        assert_eq!(Error::new(Space::User, Code::BadSize), Error(0x010003));
+        assert_eq!(Error::new(0xab, 0x1234u16), Error(0xab1234));
+    }
+}
diff --git a/crates/error/test.sh b/crates/error/test.sh
new file mode 100755
index 00000000..71993f35
--- /dev/null
+++ b/crates/error/test.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -e
+
+. "$(git rev-parse --show-toplevel)"/scripts/test-helper.sh
+
+test_helper
+
+cargo test
+cargo check --target=thumbv7em-none-eabi
+cargo check --target=wasm32-unknown-unknown
diff --git a/crates/prelude/CHANGELOG.md b/crates/prelude/CHANGELOG.md
index 58476a4c..801ba429 100644
--- a/crates/prelude/CHANGELOG.md
+++ b/crates/prelude/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Major
 
+- Remove custom error types and use `wasefire-error` instead
 - Rename `native` to `test` and use `native` for native applets
 
 ### Minor
diff --git a/crates/prelude/Cargo.lock b/crates/prelude/Cargo.lock
index a47a4a5f..10b1eb91 100644
--- a/crates/prelude/Cargo.lock
+++ b/crates/prelude/Cargo.lock
@@ -168,6 +168,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -295,6 +315,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
  "zeroize",
 ]
@@ -305,6 +326,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
@@ -329,6 +351,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-logger"
 version = "0.1.4-git"
diff --git a/crates/prelude/Cargo.toml b/crates/prelude/Cargo.toml
index 47532b76..0089d254 100644
--- a/crates/prelude/Cargo.toml
+++ b/crates/prelude/Cargo.toml
@@ -26,6 +26,7 @@ rlsf = { version = "0.2.1", default-features = false }
 sealed = { version = "0.5.0", default-features = false }
 typenum = { version = "1.17.0", default-features = false }
 wasefire-applet-api = { version = "0.6.0-git", path = "../api", features = ["wasm"] }
+wasefire-error = { version = "0.1.0-git", path = "../error" }
 wasefire-sync = { version = "0.1.0-git", path = "../sync" }
 zeroize = { version = "1.7.0", default-features = false, features = ["derive"], optional = true }
 
diff --git a/crates/prelude/src/crypto.rs b/crates/prelude/src/crypto.rs
index d41adcb9..de77dd1b 100644
--- a/crates/prelude/src/crypto.rs
+++ b/crates/prelude/src/crypto.rs
@@ -18,6 +18,3 @@ pub mod ccm;
 pub mod ec;
 pub mod gcm;
 pub mod hash;
-
-/// Errors returned by cryptographic operations.
-pub use wasefire_applet_api::crypto::Error;
diff --git a/crates/prelude/src/crypto/ccm.rs b/crates/prelude/src/crypto/ccm.rs
index 4a6cf377..0484eb08 100644
--- a/crates/prelude/src/crypto/ccm.rs
+++ b/crates/prelude/src/crypto/ccm.rs
@@ -19,7 +19,7 @@ use alloc::vec::Vec;
 
 use wasefire_applet_api::crypto::ccm as api;
 
-use super::Error;
+use crate::{convert_unit, Error};
 
 /// Whether AES-CCM is supported.
 pub fn is_supported() -> bool {
@@ -39,13 +39,13 @@ pub fn encrypt(key: &[u8; 16], nonce: &[u8; 8], clear: &[u8]) -> Result<Vec<u8>,
         cipher: cipher.as_mut_ptr(),
     };
     let api::encrypt::Results { res } = unsafe { api::encrypt(params) };
-    Error::to_result(res)?;
+    convert_unit(res)?;
     Ok(cipher)
 }
 
 /// Returns the cleartext given a ciphertext, a key, and a nonce.
 pub fn decrypt(key: &[u8; 16], nonce: &[u8; 8], cipher: &[u8]) -> Result<Vec<u8>, Error> {
-    let len = cipher.len().checked_sub(4).ok_or(Error::InvalidArgument)?;
+    let len = cipher.len().checked_sub(4).ok_or(Error::user(0))?;
     let mut clear = vec![0; len];
     let params = api::decrypt::Params {
         key: key.as_ptr(),
@@ -55,6 +55,6 @@ pub fn decrypt(key: &[u8; 16], nonce: &[u8; 8], cipher: &[u8]) -> Result<Vec<u8>
         clear: clear.as_mut_ptr(),
     };
     let api::decrypt::Results { res } = unsafe { api::decrypt(params) };
-    Error::to_result(res)?;
+    convert_unit(res)?;
     Ok(clear)
 }
diff --git a/crates/prelude/src/crypto/ec.rs b/crates/prelude/src/crypto/ec.rs
index 68a2d3f0..abf36805 100644
--- a/crates/prelude/src/crypto/ec.rs
+++ b/crates/prelude/src/crypto/ec.rs
@@ -22,7 +22,7 @@ use wasefire_applet_api::crypto::ec as api;
 use wasefire_applet_api::crypto::hash::Algorithm;
 
 use super::hash::hkdf;
-use super::Error;
+use crate::{convert_bool, convert_unit, Error};
 
 /// ECDSA private key.
 pub struct EcdsaPrivate<C: Curve>(Private<C>);
@@ -328,8 +328,7 @@ impl<T: InternalHelper> Curve for T {
             y: y.as_mut_ptr(),
         };
         let api::base_point_mul::Results { res } = unsafe { api::base_point_mul(params) };
-        Error::to_result(res)?;
-        Ok(())
+        convert_unit(res)
     }
 
     fn point_mul(
@@ -345,8 +344,7 @@ impl<T: InternalHelper> Curve for T {
             out_y: out_y.as_mut_ptr(),
         };
         let api::point_mul::Results { res } = unsafe { api::point_mul(params) };
-        Error::to_result(res)?;
-        Ok(())
+        convert_unit(res)
     }
 
     fn ecdsa_sign(
@@ -360,8 +358,7 @@ impl<T: InternalHelper> Curve for T {
             s: s.as_mut_ptr(),
         };
         let api::ecdsa_sign::Results { res } = unsafe { api::ecdsa_sign(params) };
-        Error::to_result(res)?;
-        Ok(())
+        convert_unit(res)
     }
 
     fn ecdsa_verify(
@@ -376,7 +373,7 @@ impl<T: InternalHelper> Curve for T {
             s: s.as_ptr(),
         };
         let api::ecdsa_verify::Results { res } = unsafe { api::ecdsa_verify(params) };
-        Ok(Error::to_result(res)? == 1)
+        convert_bool(res)
     }
 }
 
@@ -395,10 +392,10 @@ impl<C: Curve> Private<C> {
         let mut scalar = Int::<C>::default();
         loop {
             // TODO(#163): Use a DRBG (possibly taking it as argument).
-            crate::rng::fill_bytes(&mut scalar).map_err(|_| Error::RngFailure)?;
+            crate::rng::fill_bytes(&mut scalar)?;
             if is_zero_scalar::<C>(&scalar) {
                 // The probability is very low for this to happen during normal operation.
-                return Err(Error::RngFailure);
+                return Err(Error::world(0));
             }
             if C::is_valid_scalar(&scalar) {
                 return Ok(Self(scalar));
@@ -409,7 +406,7 @@ impl<C: Curve> Private<C> {
     /// Creates a private key from its non-zero scalar SEC1 encoding.
     fn from_non_zero_scalar(n: Int<C>) -> Result<Self, Error> {
         if is_zero_scalar::<C>(&n) || !C::is_valid_scalar(&n) {
-            return Err(Error::InvalidArgument);
+            return Err(Error::user(0));
         }
         Ok(Self(n))
     }
@@ -432,7 +429,7 @@ impl<C: Curve> Public<C> {
     /// Creates a public key from its coordinates in SEC1 encoding.
     fn from_coordinates(x: Int<C>, y: Int<C>) -> Result<Self, Error> {
         if !C::is_valid_point(&x, &y) {
-            return Err(Error::InvalidArgument);
+            return Err(Error::user(0));
         }
         Ok(Self { x, y })
     }
diff --git a/crates/prelude/src/crypto/gcm.rs b/crates/prelude/src/crypto/gcm.rs
index 07775e13..cf603a80 100644
--- a/crates/prelude/src/crypto/gcm.rs
+++ b/crates/prelude/src/crypto/gcm.rs
@@ -21,7 +21,7 @@ use alloc::vec::Vec;
 pub use rust_crypto::*;
 use wasefire_applet_api::crypto::gcm as api;
 
-use super::Error;
+use crate::{convert_unit, Error};
 
 /// Describes AES-256-GCM support.
 pub struct Support {
@@ -73,7 +73,7 @@ pub fn encrypt_mut(
     key: &[u8; 32], iv: &[u8; 12], aad: &[u8], clear: &[u8], cipher: &mut [u8], tag: &mut [u8],
 ) -> Result<(), Error> {
     if clear.len() != cipher.len() || tag.len() != tag_length() {
-        return Err(Error::InvalidArgument);
+        return Err(Error::user(0));
     }
     let params = api::encrypt::Params {
         key: key.as_ptr(),
@@ -86,8 +86,7 @@ pub fn encrypt_mut(
         tag: tag.as_mut_ptr(),
     };
     let api::encrypt::Results { res } = unsafe { api::encrypt(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 /// Encrypts and authenticates a buffer in place.
@@ -95,7 +94,7 @@ pub fn encrypt_in_place(
     key: &[u8; 32], iv: &[u8; 12], aad: &[u8], buffer: &mut [u8], tag: &mut [u8],
 ) -> Result<(), Error> {
     if tag.len() != tag_length() {
-        return Err(Error::InvalidArgument);
+        return Err(Error::user(0));
     }
     let params = api::encrypt::Params {
         key: key.as_ptr(),
@@ -108,8 +107,7 @@ pub fn encrypt_in_place(
         tag: tag.as_mut_ptr(),
     };
     let api::encrypt::Results { res } = unsafe { api::encrypt(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 /// Decrypts and authenticates a ciphertext.
@@ -126,7 +124,7 @@ pub fn decrypt_mut(
     key: &[u8; 32], iv: &[u8; 12], aad: &[u8], tag: &[u8], cipher: &[u8], clear: &mut [u8],
 ) -> Result<(), Error> {
     if cipher.len() != clear.len() || tag.len() != tag_length() {
-        return Err(Error::InvalidArgument);
+        return Err(Error::user(0));
     }
     let params = api::decrypt::Params {
         key: key.as_ptr(),
@@ -139,8 +137,7 @@ pub fn decrypt_mut(
         clear: clear.as_mut_ptr(),
     };
     let api::decrypt::Results { res } = unsafe { api::decrypt(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 /// Decrypts and authenticates a ciphertext.
@@ -148,7 +145,7 @@ pub fn decrypt_in_place(
     key: &[u8; 32], iv: &[u8; 12], aad: &[u8], tag: &[u8], buffer: &mut [u8],
 ) -> Result<(), Error> {
     if tag.len() != tag_length() {
-        return Err(Error::InvalidArgument);
+        return Err(Error::user(0));
     }
     let params = api::decrypt::Params {
         key: key.as_ptr(),
@@ -161,8 +158,7 @@ pub fn decrypt_in_place(
         clear: buffer.as_mut_ptr(),
     };
     let api::decrypt::Results { res } = unsafe { api::decrypt(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 #[cfg(feature = "rust-crypto")]
diff --git a/crates/prelude/src/crypto/hash.rs b/crates/prelude/src/crypto/hash.rs
index 5903a720..061c8507 100644
--- a/crates/prelude/src/crypto/hash.rs
+++ b/crates/prelude/src/crypto/hash.rs
@@ -20,9 +20,10 @@ use alloc::vec;
 #[cfg(feature = "rust-crypto")]
 pub use rust_crypto::*;
 use wasefire_applet_api::crypto::hash as api;
+use wasefire_error::Code;
 
 pub use self::api::Algorithm;
-use super::Error;
+use crate::{convert, convert_unit, Error};
 
 /// Hashing context.
 pub struct Digest {
@@ -39,11 +40,11 @@ impl Digest {
     /// Creates a new hashing context for the specified algorithm.
     pub fn new(algorithm: Algorithm) -> Result<Self, Error> {
         if !is_supported(algorithm) {
-            return Err(Error::Unsupported);
+            return Err(Error::world(Code::NotImplemented));
         }
         let params = api::initialize::Params { algorithm: algorithm as usize };
         let api::initialize::Results { id } = unsafe { api::initialize(params) };
-        let id = Error::to_result(id)?;
+        let id = convert(id)?;
         let len = algorithm.digest_len();
         Ok(Self { id, len })
     }
@@ -57,12 +58,12 @@ impl Digest {
     /// Finalizes the hashing context and writes the associated digest.
     pub fn finalize(mut self, digest: &mut [u8]) -> Result<(), Error> {
         if digest.len() != self.len {
-            return Err(Error::InvalidArgument);
+            return Err(Error::user(0));
         }
         let params = api::finalize::Params { id: self.id, digest: digest.as_mut_ptr() };
         let api::finalize::Results { res } = unsafe { api::finalize(params) };
         self.id = usize::MAX;
-        Error::to_result(res).map(|_| ())
+        convert_unit(res)
     }
 
     /// Writes the hash of the data for the given algorithm in the digest.
@@ -99,7 +100,7 @@ impl Hmac {
     /// Creates a new hmac context for the specified algorithm.
     pub fn new(algorithm: Algorithm, key: &[u8]) -> Result<Self, Error> {
         if !is_hmac_supported(algorithm) {
-            return Err(Error::Unsupported);
+            return Err(Error::world(Code::NotImplemented));
         }
         let params = api::hmac_initialize::Params {
             algorithm: algorithm as usize,
@@ -107,7 +108,7 @@ impl Hmac {
             key_len: key.len(),
         };
         let api::hmac_initialize::Results { id } = unsafe { api::hmac_initialize(params) };
-        let id = Error::to_result(id)?;
+        let id = convert(id)?;
         let len = algorithm.digest_len();
         Ok(Self { id, len })
     }
@@ -122,12 +123,12 @@ impl Hmac {
     /// Finalizes the hmac context and writes the associated hmac.
     pub fn finalize(mut self, hmac: &mut [u8]) -> Result<(), Error> {
         if hmac.len() != self.len {
-            return Err(Error::InvalidArgument);
+            return Err(Error::user(0));
         }
         let params = api::hmac_finalize::Params { id: self.id, hmac: hmac.as_mut_ptr() };
         let api::hmac_finalize::Results { res } = unsafe { api::hmac_finalize(params) };
         self.id = usize::MAX;
-        Error::to_result(res).map(|_| ())
+        convert_unit(res)
     }
 
     /// Writes the hmac of the data for the given algorithm.
@@ -199,7 +200,7 @@ pub fn hkdf_expand(
         okm_len: okm.len(),
     };
     let api::hkdf_expand::Results { res } = unsafe { api::hkdf_expand(params) };
-    Error::to_result(res).map(|_| ())
+    convert_unit(res)
 }
 
 /// Whether a hash algorithm is supported.
diff --git a/crates/prelude/src/lib.rs b/crates/prelude/src/lib.rs
index df48d059..123f5cfd 100644
--- a/crates/prelude/src/lib.rs
+++ b/crates/prelude/src/lib.rs
@@ -36,6 +36,7 @@
 extern crate alloc;
 
 use wasefire_applet_api as api;
+pub use wasefire_error::Error;
 
 mod allocator;
 pub mod button;
@@ -125,3 +126,24 @@ fn handle_panic(info: &core::panic::PanicInfo) -> ! {
     debug!("{}", info);
     scheduling::abort();
 }
+
+fn convert(res: isize) -> Result<usize, Error> {
+    Error::decode(res as i32).map(|x| x as usize)
+}
+
+fn convert_unit(res: isize) -> Result<(), Error> {
+    match convert(res) {
+        Ok(0) => Ok(()),
+        Ok(_) => unreachable!(),
+        Err(e) => Err(e),
+    }
+}
+
+fn convert_bool(res: isize) -> Result<bool, Error> {
+    match convert(res) {
+        Ok(0) => Ok(false),
+        Ok(1) => Ok(true),
+        Ok(_) => unreachable!(),
+        Err(e) => Err(e),
+    }
+}
diff --git a/crates/prelude/src/radio.rs b/crates/prelude/src/radio.rs
index b38caa33..84ad6b71 100644
--- a/crates/prelude/src/radio.rs
+++ b/crates/prelude/src/radio.rs
@@ -14,11 +14,4 @@
 
 //! Provides API for radio.
 
-/// Errors returned by radio operations.
-pub use wasefire_applet_api::radio::Error;
-
 pub mod ble;
-
-fn convert(len: isize) -> Result<usize, Error> {
-    Error::to_result(len)
-}
diff --git a/crates/prelude/src/radio/ble.rs b/crates/prelude/src/radio/ble.rs
index ed814c15..934f78ed 100644
--- a/crates/prelude/src/radio/ble.rs
+++ b/crates/prelude/src/radio/ble.rs
@@ -15,19 +15,17 @@
 use alloc::boxed::Box;
 
 use bytemuck::Zeroable;
+use wasefire_applet_api::radio::ble as api;
 pub use wasefire_applet_api::radio::ble::{Advertisement, Event};
-use wasefire_applet_api::radio::{ble as api, Error};
+
+use crate::{convert_bool, Error};
 
 /// Reads the next advertisement packet, if any.
 pub fn read_advertisement() -> Result<Option<Advertisement>, Error> {
     let mut result = Advertisement::zeroed();
     let params = api::read_advertisement::Params { ptr: &mut result as *mut _ as *mut u8 };
     let api::read_advertisement::Results { res } = unsafe { api::read_advertisement(params) };
-    Ok(match super::convert(res)? {
-        0 => None,
-        1 => Some(result),
-        _ => unreachable!(),
-    })
+    Ok(convert_bool(res)?.then_some(result))
 }
 
 /// Provides callback support for BLE events.
diff --git a/crates/prelude/src/rng.rs b/crates/prelude/src/rng.rs
index fa8e3327..4a214faf 100644
--- a/crates/prelude/src/rng.rs
+++ b/crates/prelude/src/rng.rs
@@ -16,16 +16,11 @@
 
 use wasefire_applet_api::rng as api;
 
-/// Error generating randomness.
-#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
-pub struct Error;
+use crate::{convert_unit, Error};
 
 /// Fills a slice with random bytes.
 pub fn fill_bytes(buf: &mut [u8]) -> Result<(), Error> {
     let params = api::fill_bytes::Params { ptr: buf.as_mut_ptr(), len: buf.len() };
     let api::fill_bytes::Results { res } = unsafe { api::fill_bytes(params) };
-    match res {
-        0 => Ok(()),
-        _ => Err(Error),
-    }
+    convert_unit(res)
 }
diff --git a/crates/prelude/src/serial.rs b/crates/prelude/src/serial.rs
index 85c857fe..19a8c862 100644
--- a/crates/prelude/src/serial.rs
+++ b/crates/prelude/src/serial.rs
@@ -20,7 +20,7 @@ use core::fmt::Debug;
 
 use sealed::sealed;
 
-use crate::scheduling;
+use crate::{scheduling, Error};
 
 /// Serial events to be notified.
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
@@ -38,22 +38,20 @@ pub enum Event {
 /// provide a unique interface to the different serials.
 #[sealed(pub(crate))]
 pub trait Serial {
-    type Error: Clone + Debug;
-
     /// Reads from the serial into a buffer without blocking.
     ///
     /// Returns how many bytes were read (and thus written to the buffer). This function does not
     /// block, so if there are no data available for read, zero is returned.
-    fn read(&self, buffer: &mut [u8]) -> Result<usize, Self::Error>;
+    fn read(&self, buffer: &mut [u8]) -> Result<usize, Error>;
 
     /// Writes from a buffer to the serial.
     ///
     /// Returns how many bytes were written (and thus read from the buffer). This function does not
     /// block, so if the serial is not ready for write, zero is returned.
-    fn write(&self, buffer: &[u8]) -> Result<usize, Self::Error>;
+    fn write(&self, buffer: &[u8]) -> Result<usize, Error>;
 
     /// Flushes the serial (in case reads or writes are buffered).
-    fn flush(&self) -> Result<(), Self::Error>;
+    fn flush(&self) -> Result<(), Error>;
 
     /// Registers a callback for an event.
     ///
@@ -63,24 +61,24 @@ pub trait Serial {
     /// concurrent calls.
     unsafe fn register(
         &self, event: Event, func: extern "C" fn(*const u8), data: *const u8,
-    ) -> Result<(), Self::Error>;
+    ) -> Result<(), Error>;
 
     /// Unregisters the callback for an event.
-    fn unregister(&self, event: Event) -> Result<(), Self::Error>;
+    fn unregister(&self, event: Event) -> Result<(), Error>;
 }
 
 /// Reads from the serial into a buffer without blocking.
 ///
 /// Returns how many bytes were read (and thus written to the buffer). This function does not
 /// block, so if there are no data available for read, zero is returned.
-pub fn read<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<usize, T::Error> {
+pub fn read<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<usize, Error> {
     serial.read(buffer)
 }
 
 /// Synchronously reads at least one byte from a serial into a buffer.
 ///
 /// This function will block if necessary.
-pub fn read_any<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<usize, T::Error> {
+pub fn read_any<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<usize, Error> {
     let mut reader = Reader::new(serial, buffer);
     scheduling::wait_until(|| !reader.is_empty());
     reader.result()
@@ -89,7 +87,7 @@ pub fn read_any<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<usize, T::Er
 /// Synchronously reads from a serial into a buffer until it is filled.
 ///
 /// This function will block if necessary.
-pub fn read_all<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<(), T::Error> {
+pub fn read_all<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<(), Error> {
     let mut reader = Reader::new(serial, buffer);
     scheduling::wait_until(|| reader.is_done());
     reader.result()?;
@@ -97,7 +95,7 @@ pub fn read_all<T: Serial>(serial: &T, buffer: &mut [u8]) -> Result<(), T::Error
 }
 
 /// Synchronously reads exactly one byte.
-pub fn read_byte<T: Serial>(serial: &T) -> Result<u8, T::Error> {
+pub fn read_byte<T: Serial>(serial: &T) -> Result<u8, Error> {
     let mut byte = 0;
     read_any(serial, core::slice::from_mut(&mut byte))?;
     Ok(byte)
@@ -107,14 +105,14 @@ pub fn read_byte<T: Serial>(serial: &T) -> Result<u8, T::Error> {
 ///
 /// Returns how many bytes were written (and thus read from the buffer). This function does not
 /// block, so if the serial is not ready for write, zero is returned.
-pub fn write<T: Serial>(serial: &T, buffer: &[u8]) -> Result<usize, T::Error> {
+pub fn write<T: Serial>(serial: &T, buffer: &[u8]) -> Result<usize, Error> {
     serial.write(buffer)
 }
 
 /// Writes at least one byte from a buffer to a serial.
 ///
 /// This function will block if necessary.
-pub fn write_any<T: Serial>(serial: &T, buffer: &[u8]) -> Result<usize, T::Error> {
+pub fn write_any<T: Serial>(serial: &T, buffer: &[u8]) -> Result<usize, Error> {
     let mut writer = Writer::new(serial, buffer);
     scheduling::wait_until(|| !writer.is_empty());
     writer.result()
@@ -123,7 +121,7 @@ pub fn write_any<T: Serial>(serial: &T, buffer: &[u8]) -> Result<usize, T::Error
 /// Writes from a buffer to a serial until everything has been written.
 ///
 /// This function will block if necessary.
-pub fn write_all<T: Serial>(serial: &T, buffer: &[u8]) -> Result<(), T::Error> {
+pub fn write_all<T: Serial>(serial: &T, buffer: &[u8]) -> Result<(), Error> {
     let mut writer = Writer::new(serial, buffer);
     scheduling::wait_until(|| writer.is_done());
     writer.result()?;
@@ -131,7 +129,7 @@ pub fn write_all<T: Serial>(serial: &T, buffer: &[u8]) -> Result<(), T::Error> {
 }
 
 /// Flushes the serial (in case reads or writes are buffered).
-pub fn flush<T: Serial>(serial: &T) -> Result<(), T::Error> {
+pub fn flush<T: Serial>(serial: &T) -> Result<(), Error> {
     serial.flush()
 }
 
@@ -156,7 +154,7 @@ impl<'a, T: Serial> Reader<'a, T> {
     }
 
     /// Returns how many bytes were read (or if an error occurred).
-    pub fn result(self) -> Result<usize, T::Error> {
+    pub fn result(self) -> Result<usize, Error> {
         self.0.result()
     }
 }
@@ -182,7 +180,7 @@ impl<'a, T: Serial> Writer<'a, T> {
     }
 
     /// Returns how many bytes were written (or if an error occurred).
-    pub fn result(self) -> Result<usize, T::Error> {
+    pub fn result(self) -> Result<usize, Error> {
         self.0.result()
     }
 }
@@ -192,7 +190,7 @@ struct Listener<'a, T: Serial> {
     // Whether the callback triggered since last operation.
     ready: &'static Cell<bool>,
     // The callback is registered as long as not done.
-    result: Result<usize, T::Error>,
+    result: Result<usize, Error>,
 }
 
 impl<'a, T: Serial> Listener<'a, T> {
@@ -219,13 +217,13 @@ impl<'a, T: Serial> Listener<'a, T> {
         !self.is_registered()
     }
 
-    fn result(mut self) -> Result<usize, T::Error> {
+    fn result(mut self) -> Result<usize, Error> {
         self.update()
     }
 
-    fn update(&mut self) -> Result<usize, T::Error> {
+    fn update(&mut self) -> Result<usize, Error> {
         if !self.is_registered() || !self.ready.replace(false) {
-            return self.result.clone();
+            return self.result;
         }
         let pos = self.result.as_mut().unwrap();
         match self.kind.update(*pos) {
@@ -235,7 +233,7 @@ impl<'a, T: Serial> Listener<'a, T> {
         if !self.is_registered() {
             self.unregister();
         }
-        self.result.clone()
+        self.result
     }
 
     fn is_registered(&self) -> bool {
@@ -287,7 +285,7 @@ impl<'a, T: Serial> Kind<'a, T> {
         }
     }
 
-    fn update(&mut self, pos: usize) -> Result<usize, T::Error> {
+    fn update(&mut self, pos: usize) -> Result<usize, Error> {
         match self {
             Kind::Reader { serial, buffer } => serial.read(&mut buffer[pos ..]),
             Kind::Writer { serial, buffer } => serial.write(&buffer[pos ..]),
diff --git a/crates/prelude/src/store.rs b/crates/prelude/src/store.rs
index 9a3c0a7b..b043dec8 100644
--- a/crates/prelude/src/store.rs
+++ b/crates/prelude/src/store.rs
@@ -18,10 +18,9 @@ use alloc::boxed::Box;
 
 use wasefire_applet_api::store as api;
 
-pub mod fragment;
+use crate::{convert_unit, Error};
 
-/// Errors returned by storage operations.
-pub use wasefire_applet_api::store::Error;
+pub mod fragment;
 
 /// Inserts an entry in the store.
 ///
@@ -31,8 +30,7 @@ pub use wasefire_applet_api::store::Error;
 pub fn insert(key: usize, value: &[u8]) -> Result<(), Error> {
     let params = api::insert::Params { key, ptr: value.as_ptr(), len: value.len() };
     let api::insert::Results { res } = unsafe { api::insert(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 /// Removes an entry from the store.
@@ -42,8 +40,7 @@ pub fn insert(key: usize, value: &[u8]) -> Result<(), Error> {
 pub fn remove(key: usize) -> Result<(), Error> {
     let params = api::remove::Params { key };
     let api::remove::Results { res } = unsafe { api::remove(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 /// Returns the value associated to a key, if any.
@@ -65,16 +62,16 @@ fn find_impl(key: usize) -> Result<Option<Box<[u8]>>, Error> {
 
 #[cfg(not(feature = "multivalue"))]
 fn find_impl(key: usize) -> Result<Option<Box<[u8]>>, Error> {
+    use crate::convert_bool;
+
     let mut ptr = core::ptr::null_mut();
     let mut len = 0;
     let params = api::find::Params { key, ptr: &mut ptr, len: &mut len };
     let api::find::Results { res } = unsafe { api::find(params) };
-    match Error::to_result(res)? {
-        0 => Ok(None),
-        1 => {
-            let ptr = unsafe { core::slice::from_raw_parts_mut(ptr, len) };
-            Ok(Some(unsafe { Box::from_raw(ptr) }))
-        }
-        _ => unreachable!(),
+    if convert_bool(res)? {
+        let ptr = unsafe { core::slice::from_raw_parts_mut(ptr, len) };
+        Ok(Some(unsafe { Box::from_raw(ptr) }))
+    } else {
+        Ok(None)
     }
 }
diff --git a/crates/prelude/src/store/fragment.rs b/crates/prelude/src/store/fragment.rs
index 437fd824..388f27ae 100644
--- a/crates/prelude/src/store/fragment.rs
+++ b/crates/prelude/src/store/fragment.rs
@@ -17,7 +17,9 @@
 use alloc::boxed::Box;
 use core::ops::Range;
 
-use wasefire_applet_api::store::{fragment as api, Error};
+use wasefire_applet_api::store::fragment as api;
+
+use crate::{convert_bool, convert_unit, Error};
 
 /// Inserts an entry in the store.
 ///
@@ -30,8 +32,7 @@ pub fn insert(keys: Range<usize>, value: &[u8]) -> Result<(), Error> {
     let params =
         api::insert::Params { keys: encode_keys(keys)?, ptr: value.as_ptr(), len: value.len() };
     let api::insert::Results { res } = unsafe { api::insert(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 /// Removes an entry from the store.
@@ -43,8 +44,7 @@ pub fn insert(keys: Range<usize>, value: &[u8]) -> Result<(), Error> {
 pub fn remove(keys: Range<usize>) -> Result<(), Error> {
     let params = api::remove::Params { keys: encode_keys(keys)? };
     let api::remove::Results { res } = unsafe { api::remove(params) };
-    Error::to_result(res)?;
-    Ok(())
+    convert_unit(res)
 }
 
 /// Returns the value associated to a key, if any.
@@ -59,18 +59,16 @@ fn find_impl(keys: Range<usize>) -> Result<Option<Box<[u8]>>, Error> {
     let mut len = 0;
     let params = api::find::Params { keys: encode_keys(keys)?, ptr: &mut ptr, len: &mut len };
     let api::find::Results { res } = unsafe { api::find(params) };
-    match Error::to_result(res)? {
-        0 => Ok(None),
-        1 => {
-            let ptr = unsafe { core::slice::from_raw_parts_mut(ptr, len) };
-            Ok(Some(unsafe { Box::from_raw(ptr) }))
-        }
-        _ => unreachable!(),
+    if convert_bool(res)? {
+        let ptr = unsafe { core::slice::from_raw_parts_mut(ptr, len) };
+        Ok(Some(unsafe { Box::from_raw(ptr) }))
+    } else {
+        Ok(None)
     }
 }
 
 fn encode_keys(keys: Range<usize>) -> Result<u32, Error> {
-    let start = u16::try_from(keys.start).map_err(|_| Error::InvalidArgument)? as u32;
-    let end = u16::try_from(keys.end).map_err(|_| Error::InvalidArgument)? as u32;
+    let start = u16::try_from(keys.start).map_err(|_| Error::user(0))? as u32;
+    let end = u16::try_from(keys.end).map_err(|_| Error::user(0))? as u32;
     Ok(end << 16 | start)
 }
diff --git a/crates/prelude/src/uart.rs b/crates/prelude/src/uart.rs
index 094962fc..53921965 100644
--- a/crates/prelude/src/uart.rs
+++ b/crates/prelude/src/uart.rs
@@ -18,10 +18,7 @@ use sealed::sealed;
 use wasefire_applet_api::uart as api;
 
 use crate::serial::Event;
-
-/// UART error.
-#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
-pub struct Error;
+use crate::{convert, Error};
 
 /// Returns the number of available UARTs on the board.
 pub fn count() -> usize {
@@ -34,8 +31,6 @@ pub struct Uart(pub usize);
 
 #[sealed]
 impl crate::serial::Serial for Uart {
-    type Error = Error;
-
     fn read(&self, buffer: &mut [u8]) -> Result<usize, Error> {
         let params =
             api::read::Params { uart: self.0, ptr: buffer.as_mut_ptr(), len: buffer.len() };
@@ -73,14 +68,6 @@ impl crate::serial::Serial for Uart {
     }
 }
 
-fn convert(code: isize) -> Result<usize, Error> {
-    if code < 0 {
-        Err(Error)
-    } else {
-        Ok(code as usize)
-    }
-}
-
 fn convert_event(event: Event) -> api::Event {
     match event {
         Event::Read => api::Event::Read,
diff --git a/crates/prelude/src/usb.rs b/crates/prelude/src/usb.rs
index cb90c031..4ff994b5 100644
--- a/crates/prelude/src/usb.rs
+++ b/crates/prelude/src/usb.rs
@@ -17,11 +17,4 @@
 //! Only serial is currently supported. HID and its derivatives (e.g. CTAP) will be added in the
 //! future.
 
-/// Errors returned by USB operations.
-pub use wasefire_applet_api::usb::Error;
-
 pub mod serial;
-
-fn convert(len: isize) -> Result<usize, Error> {
-    Error::to_result(len)
-}
diff --git a/crates/prelude/src/usb/serial.rs b/crates/prelude/src/usb/serial.rs
index f60e2517..37f5139d 100644
--- a/crates/prelude/src/usb/serial.rs
+++ b/crates/prelude/src/usb/serial.rs
@@ -18,15 +18,13 @@ use sealed::sealed;
 use wasefire_applet_api::usb::serial as api;
 
 use crate::serial::Event;
-use crate::usb::{convert, Error};
+use crate::{convert, Error};
 
 /// Implements the [`Serial`](crate::serial::Serial) interface for the USB serial.
 pub struct UsbSerial;
 
 #[sealed]
 impl crate::serial::Serial for UsbSerial {
-    type Error = Error;
-
     fn read(&self, buffer: &mut [u8]) -> Result<usize, Error> {
         let params = api::read::Params { ptr: buffer.as_mut_ptr(), len: buffer.len() };
         let api::read::Results { len } = unsafe { api::read(params) };
@@ -39,7 +37,7 @@ impl crate::serial::Serial for UsbSerial {
         convert(len)
     }
 
-    fn flush(&self) -> Result<(), Self::Error> {
+    fn flush(&self) -> Result<(), Error> {
         let api::flush::Results { res } = unsafe { api::flush() };
         convert(res).map(|_| ())
     }
diff --git a/crates/runner-host/Cargo.lock b/crates/runner-host/Cargo.lock
index c93e43ff..d403cd4d 100644
--- a/crates/runner-host/Cargo.lock
+++ b/crates/runner-host/Cargo.lock
@@ -1773,6 +1773,7 @@ dependencies = [
  "bytemuck",
  "sealed",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -1820,10 +1821,18 @@ dependencies = [
  "usb-device",
  "usbd-serial",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-logger",
  "wasefire-store",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum 0.7.1",
+]
+
 [[package]]
 name = "wasefire-interpreter"
 version = "0.2.0-git"
@@ -1853,6 +1862,7 @@ dependencies = [
  "typenum",
  "wasefire-applet-api",
  "wasefire-board-api",
+ "wasefire-error",
  "wasefire-interpreter",
  "wasefire-logger",
  "wasefire-store",
diff --git a/crates/runner-host/src/board.rs b/crates/runner-host/src/board.rs
index 63f0ba71..703afb71 100644
--- a/crates/runner-host/src/board.rs
+++ b/crates/runner-host/src/board.rs
@@ -55,7 +55,7 @@ impl Api for Board {
     fn syscall(x1: u32, x2: u32, x3: u32, x4: u32) -> Option<u32> {
         match (x1, x2, x3, x4) {
             // The syscall_test example relies on this.
-            (1, 2, 3, 4) => Some(5),
+            (0, 0, 0, x) => Some(x),
             _ => None,
         }
     }
diff --git a/crates/runner-host/src/board/timer.rs b/crates/runner-host/src/board/timer.rs
index 281287ad..ee3328d2 100644
--- a/crates/runner-host/src/board/timer.rs
+++ b/crates/runner-host/src/board/timer.rs
@@ -34,7 +34,7 @@ impl Api for Impl {
             let state = state.deref_mut();
             let timer = &mut state.timers.0[*id];
             if timer.handle.is_some() {
-                return Err(Error::User);
+                return Err(Error::user(0));
             }
             let duration = Duration::from_millis(command.duration_ms as u64);
             if command.periodic {
@@ -61,7 +61,7 @@ impl Api for Impl {
             let timer = &mut state.timers.0[*id];
             match &timer.handle {
                 Some(handle) => handle.abort(),
-                None => return Err(Error::User),
+                None => return Err(Error::user(0)),
             }
             timer.handle = None;
             Ok(())
diff --git a/crates/runner-host/src/board/uart.rs b/crates/runner-host/src/board/uart.rs
index 456a03c0..40cbc4c0 100644
--- a/crates/runner-host/src/board/uart.rs
+++ b/crates/runner-host/src/board/uart.rs
@@ -214,7 +214,7 @@ fn convert(x: Result<usize, std::io::Error>) -> Result<usize, Error> {
     match x {
         Ok(x) => Ok(x),
         Err(e) if e.kind() == ErrorKind::WouldBlock => Ok(0),
-        Err(_) => Err(Error::World),
+        Err(_) => Err(Error::world(0)),
     }
 }
 
diff --git a/crates/runner-nordic/Cargo.lock b/crates/runner-nordic/Cargo.lock
index b182b28d..0c635770 100644
--- a/crates/runner-nordic/Cargo.lock
+++ b/crates/runner-nordic/Cargo.lock
@@ -921,6 +921,7 @@ dependencies = [
  "usbd-serial",
  "wasefire-applet-api",
  "wasefire-board-api",
+ "wasefire-error",
  "wasefire-interpreter",
  "wasefire-logger",
  "wasefire-scheduler",
@@ -1160,6 +1161,7 @@ dependencies = [
  "bytemuck",
  "sealed",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -1208,10 +1210,18 @@ dependencies = [
  "usb-device",
  "usbd-serial",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-logger",
  "wasefire-store",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum 0.7.1",
+]
+
 [[package]]
 name = "wasefire-interpreter"
 version = "0.2.0-git"
@@ -1242,6 +1252,7 @@ dependencies = [
  "typenum",
  "wasefire-applet-api",
  "wasefire-board-api",
+ "wasefire-error",
  "wasefire-interpreter",
  "wasefire-logger",
  "wasefire-store",
diff --git a/crates/runner-nordic/Cargo.toml b/crates/runner-nordic/Cargo.toml
index fe8be7a2..f31b2ad4 100644
--- a/crates/runner-nordic/Cargo.toml
+++ b/crates/runner-nordic/Cargo.toml
@@ -29,6 +29,7 @@ usb-device = "0.3.1"
 usbd-serial = "0.2.0"
 wasefire-applet-api = { path = "../api" }
 wasefire-board-api = { path = "../board" }
+wasefire-error = { path = "../error" }
 wasefire-interpreter = { path = "../interpreter", optional = true }
 wasefire-logger = { path = "../logger" }
 wasefire-scheduler = { path = "../scheduler" }
diff --git a/crates/runner-nordic/src/board.rs b/crates/runner-nordic/src/board.rs
index 5273fd3b..7332b94e 100644
--- a/crates/runner-nordic/src/board.rs
+++ b/crates/runner-nordic/src/board.rs
@@ -46,7 +46,7 @@ impl board::Api for Board {
     fn syscall(x1: u32, x2: u32, x3: u32, x4: u32) -> Option<u32> {
         match (x1, x2, x3, x4) {
             // The syscall_test example relies on this.
-            (1, 2, 3, 4) => Some(5),
+            (0, 0, 0, x) => Some(x),
             _ => None,
         }
     }
diff --git a/crates/runner-nordic/src/board/crypto/ccm.rs b/crates/runner-nordic/src/board/crypto/ccm.rs
index 9008541f..82422538 100644
--- a/crates/runner-nordic/src/board/crypto/ccm.rs
+++ b/crates/runner-nordic/src/board/crypto/ccm.rs
@@ -18,6 +18,7 @@ use nrf52840_hal::ccm::CcmData;
 use typenum::{U13, U16, U4};
 use wasefire_board_api::crypto::aead::{AeadSupport, Api, Array};
 use wasefire_board_api::{Error, Support};
+use wasefire_error::Code;
 
 use crate::with_state;
 
@@ -35,14 +36,14 @@ impl Api<U16, U13> for Impl {
         tag: &mut Array<U4>,
     ) -> Result<(), Error> {
         if aad != [0] {
-            return Err(Error::User);
+            return Err(Error::user(Code::BadSize));
         }
         let clear = match clear {
             Some(x) => x,
             None => cipher,
         };
         if 251 < clear.len() || cipher.len() != clear.len() {
-            return Err(Error::User);
+            return Err(Error::user(Code::BadSize));
         }
         let len = clear.len();
         let mut ccm_data = CcmData::new((*key).into(), truncate_iv(iv));
@@ -58,7 +59,7 @@ impl Api<U16, U13> for Impl {
                 cipher.copy_from_slice(&cipher_packet[3 ..][.. len]);
                 tag.copy_from_slice(&cipher_packet[3 + len ..]);
             }
-            Err(_) => return Err(Error::World),
+            Err(_) => return Err(Error::world(0)),
         }
         Ok(())
     }
@@ -68,14 +69,14 @@ impl Api<U16, U13> for Impl {
         clear: &mut [u8],
     ) -> Result<(), Error> {
         if aad != [0] {
-            return Err(Error::User);
+            return Err(Error::user(Code::BadSize));
         }
         let cipher = match cipher {
             Some(x) => x,
             None => clear,
         };
         if 251 < clear.len() || cipher.len() != clear.len() {
-            return Err(Error::User);
+            return Err(Error::user(Code::BadSize));
         }
         let len = clear.len();
         let mut ccm_data = CcmData::new((*key).into(), truncate_iv(iv));
@@ -89,7 +90,7 @@ impl Api<U16, U13> for Impl {
             state.ccm.decrypt_packet(&mut ccm_data, &mut clear_packet, &cipher_packet, &mut scratch)
         }) {
             Ok(()) => clear.copy_from_slice(&clear_packet[3 ..]),
-            Err(_) => return Err(Error::World),
+            Err(_) => return Err(Error::world(0)),
         }
         Ok(())
     }
diff --git a/crates/runner-nordic/src/board/gpio.rs b/crates/runner-nordic/src/board/gpio.rs
index b6686d28..1b8407aa 100644
--- a/crates/runner-nordic/src/board/gpio.rs
+++ b/crates/runner-nordic/src/board/gpio.rs
@@ -22,6 +22,7 @@ use nrf52840_hal::pac::generic::Reg;
 use nrf52840_hal::pac::p0::pin_cnf::PIN_CNF_SPEC;
 use wasefire_board_api::gpio::{Api, Config, InputConfig, OutputConfig};
 use wasefire_board_api::{Error, Id, Support};
+use wasefire_error::Code;
 
 use crate::with_state;
 
@@ -55,14 +56,14 @@ impl Api for Impl {
             match &state.gpios[*gpio] {
                 Gpio::Invalid => unreachable!(),
                 Gpio::Disconnected(_) | Gpio::OutputPushPull(_) | Gpio::OutputOpenDrain(_) => {
-                    return Err(Error::User);
+                    return Err(Error::user(Code::BadState));
                 }
                 Gpio::InputFloating(x) => x.is_high(),
                 Gpio::InputPullDown(x) => x.is_high(),
                 Gpio::InputPullUp(x) => x.is_high(),
                 Gpio::OutputOpenDrainIO(x) => x.is_high(),
             }
-            .map_err(|_| Error::World)
+            .map_err(|_| Error::world(0))
         })
     }
 
@@ -74,12 +75,12 @@ impl Api for Impl {
                 Gpio::Disconnected(_)
                 | Gpio::InputFloating(_)
                 | Gpio::InputPullDown(_)
-                | Gpio::InputPullUp(_) => return Err(Error::User),
+                | Gpio::InputPullUp(_) => return Err(Error::user(Code::BadState)),
                 Gpio::OutputPushPull(x) => x.set_state(value),
                 Gpio::OutputOpenDrain(x) => x.set_state(value),
                 Gpio::OutputOpenDrainIO(x) => x.set_state(value),
             }
-            .map_err(|_| Error::World)
+            .map_err(|_| Error::world(0))
         })
     }
 }
@@ -121,7 +122,7 @@ fn configure<MODE>(
         (InputConfig::Disabled, OutputConfig::PushPull) => {
             (Gpio::OutputPushPull(pin.into_push_pull_output(initial)), Ok(()))
         }
-        (_, OutputConfig::PushPull) => (wrap(pin), Err(Error::User)),
+        (_, OutputConfig::PushPull) => (wrap(pin), Err(Error::user(0))),
         (InputConfig::Disabled, OutputConfig::OpenDrain) => (
             Gpio::OutputOpenDrain(
                 pin.into_open_drain_output(OpenDrainConfig::Standard0Disconnect1, initial),
@@ -134,7 +135,7 @@ fn configure<MODE>(
             ),
             Ok(()),
         ),
-        (InputConfig::PullDown, OutputConfig::OpenDrain) => (wrap(pin), Err(Error::User)),
+        (InputConfig::PullDown, OutputConfig::OpenDrain) => (wrap(pin), Err(Error::user(0))),
         (InputConfig::PullUp, OutputConfig::OpenDrain) => {
             let pin =
                 pin.into_open_drain_input_output(OpenDrainConfig::Standard0Disconnect1, initial);
@@ -159,7 +160,7 @@ fn configure<MODE>(
             pin_cnf(&pin).modify(|_, w| w.pull().pulldown());
             (Gpio::OutputOpenDrainIO(pin), Ok(()))
         }
-        (InputConfig::PullUp, OutputConfig::OpenSource) => (wrap(pin), Err(Error::User)),
+        (InputConfig::PullUp, OutputConfig::OpenSource) => (wrap(pin), Err(Error::user(0))),
     }
 }
 
diff --git a/crates/runner-nordic/src/board/led.rs b/crates/runner-nordic/src/board/led.rs
index dfcf3318..1a78e3c6 100644
--- a/crates/runner-nordic/src/board/led.rs
+++ b/crates/runner-nordic/src/board/led.rs
@@ -28,7 +28,7 @@ impl Api for Impl {
     fn get(id: Id<Self>) -> Result<bool, Error> {
         with_state(|state| {
             let led = &mut state.leds[*id];
-            led.is_set_low().map_err(|_| Error::World)
+            led.is_set_low().map_err(|_| Error::world(0))
         })
     }
 
@@ -39,7 +39,7 @@ impl Api for Impl {
                 false => led.set_high(),
                 true => led.set_low(),
             }
-            .map_err(|_| Error::World)
+            .map_err(|_| Error::world(0))
         })
     }
 }
diff --git a/crates/runner-nordic/src/board/uart.rs b/crates/runner-nordic/src/board/uart.rs
index 7f66464e..d911d994 100644
--- a/crates/runner-nordic/src/board/uart.rs
+++ b/crates/runner-nordic/src/board/uart.rs
@@ -173,7 +173,7 @@ impl Api for Impl {
             return Ok(0);
         }
         if EASY_DMA_SIZE < input.len() || !in_ram(input) {
-            return Err(Error::User);
+            return Err(Error::user(0));
         }
         with_state(|state| {
             let uart = state.uarts.get(uart);
diff --git a/crates/scheduler/CHANGELOG.md b/crates/scheduler/CHANGELOG.md
index 6d7b9635..163450ed 100644
--- a/crates/scheduler/CHANGELOG.md
+++ b/crates/scheduler/CHANGELOG.md
@@ -8,6 +8,7 @@
 
 ### Minor
 
+- Migrate to `wasefire-error`
 - Support `gpio` module
 - Support `platform::version()`
 - Support `radio::ble` module
@@ -95,4 +96,4 @@
 
 ## 0.1.0
 
-<!-- Increment to skip CHANGELOG.md test: 24 -->
+<!-- Increment to skip CHANGELOG.md test: 25 -->
diff --git a/crates/scheduler/Cargo.lock b/crates/scheduler/Cargo.lock
index 6ae44156..81838886 100644
--- a/crates/scheduler/Cargo.lock
+++ b/crates/scheduler/Cargo.lock
@@ -516,6 +516,7 @@ dependencies = [
  "bytemuck",
  "sealed",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -553,10 +554,18 @@ dependencies = [
  "usb-device",
  "usbd-serial",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-logger",
  "wasefire-store",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum 0.7.1",
+]
+
 [[package]]
 name = "wasefire-interpreter"
 version = "0.2.0-git"
@@ -588,6 +597,7 @@ dependencies = [
  "typenum",
  "wasefire-applet-api",
  "wasefire-board-api",
+ "wasefire-error",
  "wasefire-interpreter",
  "wasefire-logger",
  "wasefire-store",
diff --git a/crates/scheduler/Cargo.toml b/crates/scheduler/Cargo.toml
index ac3cafd2..0a279d57 100644
--- a/crates/scheduler/Cargo.toml
+++ b/crates/scheduler/Cargo.toml
@@ -25,6 +25,7 @@ portable-atomic = { version = "1.6.0", default-features = false }
 typenum = { version = "1.17.0", default-features = false }
 wasefire-applet-api = { version = "0.6.0-git", path = "../api", features = ["host"] }
 wasefire-board-api = { version = "0.6.0-git", path = "../board" }
+wasefire-error = { version = "0.1.0-git", path = "../error" }
 wasefire-logger = { version = "0.1.4-git", path = "../logger" }
 wasefire-store = { version = "0.2.3-git", path = "../store" }
 wasefire-sync = { version = "0.1.0-git", path = "../sync" }
diff --git a/crates/scheduler/src/call/crypto/ccm.rs b/crates/scheduler/src/call/crypto/ccm.rs
index 806c6df8..94a039af 100644
--- a/crates/scheduler/src/call/crypto/ccm.rs
+++ b/crates/scheduler/src/call/crypto/ccm.rs
@@ -46,10 +46,7 @@ fn encrypt<B: Board>(mut call: SchedulerCall<B, api::encrypt::Sig>) {
         let clear = Some(memory.get(*clear, *len)?);
         let (cipher, tag) = memory.get_mut(*cipher, *len + 4)?.split_at_mut(*len as usize);
         let tag = tag.into();
-        let res = match board::crypto::Aes128Ccm::<B>::encrypt(key, &iv, aad, clear, cipher, tag) {
-            Ok(()) => 0u32.into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let res = board::crypto::Aes128Ccm::<B>::encrypt(key, &iv, aad, clear, cipher, tag).into();
         api::encrypt::Results { res }
     };
     call.reply(results);
@@ -68,10 +65,7 @@ fn decrypt<B: Board>(mut call: SchedulerCall<B, api::decrypt::Sig>) {
         let cipher = Some(cipher);
         let tag = tag.into();
         let clear = memory.get_mut(*clear, *len)?;
-        let res = match board::crypto::Aes128Ccm::<B>::decrypt(key, &iv, aad, cipher, tag, clear) {
-            Ok(()) => 0u32.into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let res = board::crypto::Aes128Ccm::<B>::decrypt(key, &iv, aad, cipher, tag, clear).into();
         api::decrypt::Results { res }
     };
     call.reply(results);
diff --git a/crates/scheduler/src/call/crypto/ec.rs b/crates/scheduler/src/call/crypto/ec.rs
index 9591b65c..af9f4171 100644
--- a/crates/scheduler/src/call/crypto/ec.rs
+++ b/crates/scheduler/src/call/crypto/ec.rs
@@ -92,19 +92,13 @@ fn base_point_mul<B: Board>(mut call: SchedulerCall<B, api::base_point_mul::Sig>
                 let n = memory.get_array::<32>(*n)?.into();
                 let x = memory.get_array_mut::<32>(*x)?.into();
                 let y = memory.get_array_mut::<32>(*y)?.into();
-                match board::crypto::P256::<B>::base_point_mul(n, x, y) {
-                    Ok(()) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P256::<B>::base_point_mul(n, x, y)
             }
             Curve::P384 => {
                 let n = memory.get_array::<48>(*n)?.into();
                 let x = memory.get_array_mut::<48>(*x)?.into();
                 let y = memory.get_array_mut::<48>(*y)?.into();
-                match board::crypto::P384::<B>::base_point_mul(n, x, y) {
-                    Ok(()) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P384::<B>::base_point_mul(n, x, y)
             }
         };
         api::base_point_mul::Results { res: res.into() }
@@ -124,10 +118,7 @@ fn point_mul<B: Board>(mut call: SchedulerCall<B, api::point_mul::Sig>) {
                 let in_y = memory.get_array::<32>(*in_y)?.into();
                 let out_x = memory.get_array_mut::<32>(*out_x)?.into();
                 let out_y = memory.get_array_mut::<32>(*out_y)?.into();
-                match board::crypto::P256::<B>::point_mul(n, in_x, in_y, out_x, out_y) {
-                    Ok(()) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P256::<B>::point_mul(n, in_x, in_y, out_x, out_y)
             }
             Curve::P384 => {
                 let n = memory.get_array::<48>(*n)?.into();
@@ -135,10 +126,7 @@ fn point_mul<B: Board>(mut call: SchedulerCall<B, api::point_mul::Sig>) {
                 let in_y = memory.get_array::<48>(*in_y)?.into();
                 let out_x = memory.get_array_mut::<48>(*out_x)?.into();
                 let out_y = memory.get_array_mut::<48>(*out_y)?.into();
-                match board::crypto::P384::<B>::point_mul(n, in_x, in_y, out_x, out_y) {
-                    Ok(()) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P384::<B>::point_mul(n, in_x, in_y, out_x, out_y)
             }
         };
         api::point_mul::Results { res: res.into() }
@@ -157,20 +145,14 @@ fn ecdsa_sign<B: Board>(mut call: SchedulerCall<B, api::ecdsa_sign::Sig>) {
                 let message = memory.get_array::<32>(*message)?.into();
                 let r = memory.get_array_mut::<32>(*r)?.into();
                 let s = memory.get_array_mut::<32>(*s)?.into();
-                match board::crypto::P256::<B>::ecdsa_sign(key, message, r, s) {
-                    Ok(()) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P256::<B>::ecdsa_sign(key, message, r, s)
             }
             Curve::P384 => {
                 let key = memory.get_array::<48>(*key)?.into();
                 let message = memory.get_array::<48>(*message)?.into();
                 let r = memory.get_array_mut::<48>(*r)?.into();
                 let s = memory.get_array_mut::<48>(*s)?.into();
-                match board::crypto::P384::<B>::ecdsa_sign(key, message, r, s) {
-                    Ok(()) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P384::<B>::ecdsa_sign(key, message, r, s)
             }
         };
         api::ecdsa_sign::Results { res: res.into() }
@@ -190,11 +172,7 @@ fn ecdsa_verify<B: Board>(mut call: SchedulerCall<B, api::ecdsa_verify::Sig>) {
                 let y = memory.get_array::<32>(*y)?.into();
                 let r = memory.get_array::<32>(*r)?.into();
                 let s = memory.get_array::<32>(*s)?.into();
-                match board::crypto::P256::<B>::ecdsa_verify(message, x, y, r, s) {
-                    Ok(true) => 1u32,
-                    Ok(false) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P256::<B>::ecdsa_verify(message, x, y, r, s)
             }
             Curve::P384 => {
                 let message = memory.get_array::<48>(*message)?.into();
@@ -202,11 +180,7 @@ fn ecdsa_verify<B: Board>(mut call: SchedulerCall<B, api::ecdsa_verify::Sig>) {
                 let y = memory.get_array::<48>(*y)?.into();
                 let r = memory.get_array::<48>(*r)?.into();
                 let s = memory.get_array::<48>(*s)?.into();
-                match board::crypto::P384::<B>::ecdsa_verify(message, x, y, r, s) {
-                    Ok(true) => 1u32,
-                    Ok(false) => 0u32,
-                    Err(_) => u32::MAX,
-                }
+                board::crypto::P384::<B>::ecdsa_verify(message, x, y, r, s)
             }
         };
         api::ecdsa_verify::Results { res: res.into() }
diff --git a/crates/scheduler/src/call/crypto/gcm.rs b/crates/scheduler/src/call/crypto/gcm.rs
index 82e70bfc..d45e57f1 100644
--- a/crates/scheduler/src/call/crypto/gcm.rs
+++ b/crates/scheduler/src/call/crypto/gcm.rs
@@ -55,10 +55,7 @@ fn encrypt<B: Board>(mut call: SchedulerCall<B, api::encrypt::Sig>) {
         let cipher = memory.get_mut(*cipher, *length)?;
         let tag_len = tag_len::<B>() as u32;
         let tag = memory.get_mut(*tag, tag_len)?.into();
-        let res = match board::crypto::Aes256Gcm::<B>::encrypt(key, iv, aad, clear, cipher, tag) {
-            Ok(()) => 0u32.into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let res = board::crypto::Aes256Gcm::<B>::encrypt(key, iv, aad, clear, cipher, tag).into();
         api::encrypt::Results { res }
     };
     call.reply(results);
@@ -77,10 +74,7 @@ fn decrypt<B: Board>(mut call: SchedulerCall<B, api::decrypt::Sig>) {
         let tag = memory.get(*tag, tag_len)?.into();
         let cipher = memory.get_opt(*cipher, *length)?;
         let clear = memory.get_mut(*clear, *length)?;
-        let res = match board::crypto::Aes256Gcm::<B>::decrypt(key, iv, aad, cipher, tag, clear) {
-            Ok(()) => 0u32.into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let res = board::crypto::Aes256Gcm::<B>::decrypt(key, iv, aad, cipher, tag, clear).into();
         api::decrypt::Results { res }
     };
     call.reply(results);
diff --git a/crates/scheduler/src/call/crypto/hash.rs b/crates/scheduler/src/call/crypto/hash.rs
index 29c7fd26..fa08cd08 100644
--- a/crates/scheduler/src/call/crypto/hash.rs
+++ b/crates/scheduler/src/call/crypto/hash.rs
@@ -14,9 +14,9 @@
 
 use digest::{FixedOutput, InvalidLength, KeyInit, Output, Update};
 use generic_array::GenericArray;
-use wasefire_applet_api::crypto as crypto_api;
 use wasefire_applet_api::crypto::hash::{self as api, Algorithm, Api};
 use wasefire_board_api::{self as board, Api as Board, Support};
+use wasefire_error::Error;
 
 use crate::applet::store::{MemoryApi, StoreApi};
 use crate::applet::HashContext;
@@ -191,7 +191,7 @@ fn hkdf_expand<B: Board>(mut call: SchedulerCall<B, api::hkdf_expand::Sig>) {
         };
         let res = match res {
             Ok(()) => 0.into(),
-            Err(InvalidLength) => crypto_api::Error::InvalidArgument.into(),
+            Err(InvalidLength) => Error::user(0).into(),
         };
         api::hkdf_expand::Results { res }
     };
diff --git a/crates/scheduler/src/call/radio/ble.rs b/crates/scheduler/src/call/radio/ble.rs
index f2613c57..7cb5347e 100644
--- a/crates/scheduler/src/call/radio/ble.rs
+++ b/crates/scheduler/src/call/radio/ble.rs
@@ -65,10 +65,7 @@ fn read_advertisement<B: Board>(mut call: SchedulerCall<B, api::read_advertiseme
     let memory = scheduler.applet.memory();
     let results = try {
         let packet = memory.from_bytes_mut::<Advertisement>(*ptr)?;
-        let res = match board::radio::Ble::<B>::read_advertisement(packet) {
-            Ok(read) => (read as u32).into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let res = board::radio::Ble::<B>::read_advertisement(packet).map(|x| x as u32).into();
         api::read_advertisement::Results { res }
     };
     call.reply(results);
diff --git a/crates/scheduler/src/call/store.rs b/crates/scheduler/src/call/store.rs
index 8e9f05e7..12bebeee 100644
--- a/crates/scheduler/src/call/store.rs
+++ b/crates/scheduler/src/call/store.rs
@@ -14,6 +14,7 @@
 
 use wasefire_applet_api::store::{self as api, Api};
 use wasefire_board_api::Api as Board;
+use wasefire_error::{Code, Error};
 use wasefire_store::StoreError;
 
 use crate::applet::store::MemoryApi;
@@ -91,12 +92,11 @@ fn find<B: Board>(mut call: SchedulerCall<B, api::find::Sig>) {
     call.reply(results);
 }
 
-fn convert(err: StoreError) -> api::Error {
+fn convert(err: StoreError) -> Error {
     match err {
-        StoreError::InvalidArgument => api::Error::InvalidArgument,
-        StoreError::NoCapacity => api::Error::NoCapacity,
-        StoreError::NoLifetime => api::Error::NoLifetime,
-        StoreError::StorageError => api::Error::StorageError,
-        StoreError::InvalidStorage => api::Error::InvalidStorage,
+        StoreError::InvalidArgument => Error::user(0),
+        StoreError::NoCapacity | StoreError::NoLifetime => Error::user(Code::NotEnough),
+        StoreError::StorageError => Error::world(0),
+        StoreError::InvalidStorage => Error::world(Code::BadState),
     }
 }
diff --git a/crates/scheduler/src/call/usb/serial.rs b/crates/scheduler/src/call/usb/serial.rs
index 90e2931f..c324ddc7 100644
--- a/crates/scheduler/src/call/usb/serial.rs
+++ b/crates/scheduler/src/call/usb/serial.rs
@@ -37,10 +37,7 @@ fn read<B: Board>(mut call: SchedulerCall<B, api::read::Sig>) {
     let memory = scheduler.applet.memory();
     let results = try {
         let output = memory.get_mut(*ptr, *len)?;
-        let len = match board::usb::Serial::<B>::read(output) {
-            Ok(len) => (len as u32).into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let len = board::usb::Serial::<B>::read(output).map(|x| x as u32).into();
         api::read::Results { len }
     };
     call.reply(results);
@@ -52,10 +49,7 @@ fn write<B: Board>(mut call: SchedulerCall<B, api::write::Sig>) {
     let memory = scheduler.applet.memory();
     let results = try {
         let input = memory.get(*ptr, *len)?;
-        let len = match board::usb::Serial::<B>::write(input) {
-            Ok(len) => (len as u32).into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let len = board::usb::Serial::<B>::write(input).map(|x| x as u32).into();
         api::write::Results { len }
     };
     call.reply(results);
@@ -94,10 +88,7 @@ fn unregister<B: Board>(mut call: SchedulerCall<B, api::unregister::Sig>) {
 fn flush<B: Board>(call: SchedulerCall<B, api::flush::Sig>) {
     let api::flush::Params {} = call.read();
     let results = try {
-        let res = match board::usb::Serial::<B>::flush() {
-            Ok(()) => 0.into(),
-            Err(_) => u32::MAX.into(),
-        };
+        let res = board::usb::Serial::<B>::flush().into();
         api::flush::Results { res }
     };
     call.reply(results);
diff --git a/crates/scheduler/src/lib.rs b/crates/scheduler/src/lib.rs
index 8a42bafc..1db27009 100644
--- a/crates/scheduler/src/lib.rs
+++ b/crates/scheduler/src/lib.rs
@@ -31,7 +31,7 @@ use event::Key;
 use wasefire_applet_api::{self as api, Api, ArrayU32, Dispatch, Id, Signature};
 use wasefire_board_api::{self as board, Api as Board, Singleton, Support};
 #[cfg(feature = "wasm")]
-use wasefire_interpreter::{self as interpreter, Call, Error, Module, RunAnswer, Val};
+use wasefire_interpreter::{self as interpreter, Call, Module, RunAnswer, Val};
 use {wasefire_logger as log, wasefire_store as store};
 
 use crate::applet::store::{Memory, Store, StoreApi};
@@ -394,7 +394,7 @@ impl<B: Board> Scheduler<B> {
                 self.applet.done();
             }
             Ok(RunAnswer::Host) => (),
-            Err(Error::Trap) => applet_trapped::<B>(None),
+            Err(interpreter::Error::Trap) => applet_trapped::<B>(None),
             Err(e) => log::panic!("{}", log::Debug2Format(&e)),
         }
     }
@@ -417,8 +417,8 @@ fn applet_trapped<B: Board>(reason: Option<&'static str>) -> ! {
 
 pub struct Trap;
 
-impl From<()> for Trap {
-    fn from(_: ()) -> Self {
+impl From<wasefire_error::Error> for Trap {
+    fn from(_: wasefire_error::Error) -> Self {
         Trap
     }
 }
diff --git a/crates/stub/CHANGELOG.md b/crates/stub/CHANGELOG.md
index 3a064e18..f36b0d50 100644
--- a/crates/stub/CHANGELOG.md
+++ b/crates/stub/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Minor
 
+- Migrate to `wasefire-error`
 - Use `wasefire-logger` for panics
 
 ### Patch
diff --git a/crates/stub/Cargo.lock b/crates/stub/Cargo.lock
index 5fc2ef9e..fa898cb6 100644
--- a/crates/stub/Cargo.lock
+++ b/crates/stub/Cargo.lock
@@ -282,6 +282,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "p256"
 version = "0.13.2"
@@ -465,6 +485,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
@@ -489,6 +510,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-logger"
 version = "0.1.4-git"
@@ -510,6 +538,7 @@ dependencies = [
  "sha2",
  "signature",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
diff --git a/crates/stub/Cargo.toml b/crates/stub/Cargo.toml
index 4bd530c5..1125cba4 100644
--- a/crates/stub/Cargo.toml
+++ b/crates/stub/Cargo.toml
@@ -25,4 +25,5 @@ rand = { version = "0.8.5", default-features = false, features = ["std", "std_rn
 sha2 = { version = "0.10.8", default-features = false }
 signature = { version = "2.2.0", default-features = false }
 wasefire-applet-api = { version = "0.6.0-git", path = "../api", features = ["native", "wasm"] }
+wasefire-error = { version = "0.1.0-git", path = "../error" }
 wasefire-logger = { version = "0.1.4-git", path = "../logger" }
diff --git a/crates/stub/src/crypto/hash.rs b/crates/stub/src/crypto/hash.rs
index 54d4dd10..2806b89f 100644
--- a/crates/stub/src/crypto/hash.rs
+++ b/crates/stub/src/crypto/hash.rs
@@ -19,7 +19,8 @@ use digest::{FixedOutput, Update};
 use hkdf::{Hkdf, HmacImpl};
 use hmac::Hmac;
 use sha2::{Sha256, Sha384};
-use wasefire_applet_api::crypto::{hash as api, Error};
+use wasefire_applet_api::crypto::hash as api;
+use wasefire_error::Error;
 use wasefire_logger as log;
 
 enum Context {
@@ -113,7 +114,7 @@ unsafe extern "C" fn env_chj(
     };
     let id = match context {
         Ok(context) => CONTEXTS.lock().unwrap().insert(context) as isize,
-        Err(_) => Error::InvalidArgument.into(),
+        Err(_) => Error::encode(Err(Error::user(0))) as isize,
     };
     api::hmac_initialize::Results { id }
 }
@@ -156,16 +157,13 @@ unsafe extern "C" fn env_che(params: api::hkdf_expand::Params) -> api::hkdf_expa
         api::Algorithm::Sha256 => hkdf::<Sha256, Hmac<Sha256>>(prk, info, okm),
         api::Algorithm::Sha384 => hkdf::<Sha384, Hmac<Sha384>>(prk, info, okm),
     };
-    let res = match res {
-        Ok(()) => 0,
-        Err(err) => err.into(),
-    };
+    let res = Error::encode(res.map(|()| 0)) as isize;
     api::hkdf_expand::Results { res }
 }
 
 fn hkdf<H: OutputSizeUser, I: HmacImpl<H>>(
     prk: &[u8], info: &[u8], okm: &mut [u8],
 ) -> Result<(), Error> {
-    let hkdf = Hkdf::<H, I>::from_prk(prk).map_err(|_| Error::InvalidArgument)?;
-    hkdf.expand(info, okm).map_err(|_| Error::InvalidArgument)
+    let hkdf = Hkdf::<H, I>::from_prk(prk).map_err(|_| Error::user(0))?;
+    hkdf.expand(info, okm).map_err(|_| Error::user(0))
 }
diff --git a/examples/assemblyscript/api.ts b/examples/assemblyscript/api.ts
index e36a41f2..9fcfdf5b 100644
--- a/examples/assemblyscript/api.ts
+++ b/examples/assemblyscript/api.ts
@@ -111,18 +111,6 @@
 
 // START OF MODULE crypto
 // Cryptographic operations.
-  // Describes errors on cryptographic operations.
-  enum crypto_Error {
-    // A function pre-condition was broken.
-    InvalidArgument = 0,
-
-    // An operation is unsupported.
-    Unsupported = 1,
-
-    // An RNG operation failed.
-    RngFailure = 2,
-  }
-
   // START OF MODULE crypto_ccm
   // AES-CCM according to Bluetooth.
     // Whether AES-CCM is supported.
@@ -155,8 +143,7 @@
       //
       // Its length must be `len + 4` bytes.
       cipher: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
 
     // Decrypts a cipher text given a key and IV.
@@ -183,8 +170,7 @@
       //
       // Its length must be provided in the `len` field.
       clear: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
   // END OF MODULE crypto_ccm
 
@@ -245,8 +231,7 @@
 
       // The y coordinate in SEC1 encoding.
       y: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
 
     // Performs point multiplication.
@@ -269,8 +254,7 @@
 
       // The y coordinate of the output point in SEC1 encoding.
       out_y: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
 
     // Signs a message with ECDSA.
@@ -290,8 +274,7 @@
 
       // The s signature component in SEC1 encoding.
       s: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
 
     // Verifies an ECDSA signature.
@@ -314,8 +297,7 @@
 
       // The s signature component in SEC1 encoding.
       s: usize,
-    // 1 if the signature is valid, 0 if invalid, and bitwise complement of
-    // [`Error`](crate::crypto::Error) otherwise.
+    // One if the signature is valid. Zero if invalid. Negative on error.
     ): isize
   // END OF MODULE crypto_ec
 
@@ -376,8 +358,7 @@
 
       // The authentication tag (see [`super::tag_length()`]).
       tag: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
 
     // Decrypts and authenticates a cipher text with associated data given a key and IV.
@@ -409,8 +390,7 @@
 
       // The clear text.
       clear: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
   // END OF MODULE crypto_gcm
 
@@ -438,8 +418,7 @@
     export declare function crypto_hash_initialize(
       // The hash algorithm.
       algorithm: usize,
-    // A non-negative identifier on success, bitwise complement of
-    // [`Error`](crate::crypto::Error) otherwise.
+    // Negative on error. The identifier otherwise.
     ): isize
 
     // Updates a hash.
@@ -473,8 +452,7 @@
       // The pointer may be null, in which case this function deallocates the identifier
       // without computing the digest.
       digest: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
 
     // Whether the algorithm is supported for hmac.
@@ -498,8 +476,7 @@
       //
       // If greater than 64 bytes, the key will be itself hashed.
       key_len: usize,
-    // A non-negative identifier on success, bitwise complement of
-    // [`Error`](crate::crypto::Error) otherwise.
+    // Negative on error. The identifier otherwise.
     ): isize
 
     // Updates an hmac.
@@ -533,8 +510,7 @@
       // The pointer may be null, in which case this function deallocates the identifier
       // without computing the hmac.
       hmac: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative otherwise.
     ): isize
 
     // Whether the algorithm is supported for hkdf.
@@ -576,8 +552,7 @@
       //
       // Must be at most 255 times the output length of the hash algorithm.
       okm_len: usize,
-    // Zero on success, bitwise complement of [`Error`](crate::crypto::Error)
-    // otherwise.
+    // Zero on success. Negative on error.
     ): isize
   // END OF MODULE crypto_hash
 // END OF MODULE crypto
@@ -852,11 +827,6 @@
 
 // START OF MODULE radio
 // Radio operations.
-  // Describes errors on radio operations.
-  enum radio_Error {
-    Unknown = 0,
-  }
-
   // START OF MODULE radio_ble
   // Bluetooth Low Energy (BLE) operations.
     // BLE events.
@@ -889,8 +859,8 @@
     export declare function radio_ble_read_advertisement(
       // Pointer to the [`super::Advertisement`] packet.
       ptr: usize,
-    // One if a packet was read. Zero if there was no packet to read. Otherwise
-    // complement of error number.
+    // One if a packet was read. Zero if there was no packet to read. Negative on
+    // error.
     ): isize
 
     // Register a handler for radio events.
@@ -957,24 +927,6 @@
 
 // START OF MODULE store
 // Persistent storage operations.
-  // Describes errors interacting with the store.
-  enum store_Error {
-    // A function pre-condition was broken.
-    InvalidArgument = 0,
-
-    // The store is full.
-    NoCapacity = 1,
-
-    // The store reached its end of life.
-    NoLifetime = 2,
-
-    // An operation to the underlying storage failed.
-    StorageError = 3,
-
-    // The underlying storage doesn't match the store invariant.
-    InvalidStorage = 4,
-  }
-
   // Inserts an entry in the store.
   //
   // If an entry for that key was already present, it is overwritten.
@@ -990,7 +942,7 @@
 
     // Length of the value.
     len: usize,
-  // Zero for success. Otherwise complement of error number.
+  // Zero for success. Negative on error.
   ): isize
 
   // Removes an entry from the store.
@@ -1000,7 +952,7 @@
   export declare function store_remove(
     // Key of the entry.
     key: usize,
-  // Zero for success. Otherwise complement of error number.
+  // Zero for success. Negative on error.
   ): isize
 
   // Finds an entry in the store, if any.
@@ -1017,7 +969,7 @@
 
     // Where to write the length of the value, if found.
     len: usize,
-  // One if found. Zero if not found. Otherwise complement of error number.
+  // One if found. Zero if not found. Negative on error.
   ): isize
 
   // START OF MODULE store_fragment
@@ -1154,11 +1106,6 @@
 
 // START OF MODULE usb
 // USB operations.
-  // Describes errors on USB operations.
-  enum usb_Error {
-    Unknown = 0,
-  }
-
   // START OF MODULE usb_serial
     // Reads from USB serial into a buffer.
     @external("env", "usr")
@@ -1216,7 +1163,7 @@
     // Flushs the USB serial.
     @external("env", "usf")
     export declare function usb_serial_flush(
-    // Zero on success, -1 on error.
+    // Zero on success. Negative on error.
     ): isize
   // END OF MODULE usb_serial
 // END OF MODULE usb
diff --git a/examples/rust/blink/Cargo.lock b/examples/rust/blink/Cargo.lock
index 94dcd99d..4220540a 100644
--- a/examples/rust/blink/Cargo.lock
+++ b/examples/rust/blink/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/blink_periodic/Cargo.lock b/examples/rust/blink_periodic/Cargo.lock
index efe3f359..f167182b 100644
--- a/examples/rust/blink_periodic/Cargo.lock
+++ b/examples/rust/blink_periodic/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/button/Cargo.lock b/examples/rust/button/Cargo.lock
index 1cd82963..4531ad4a 100644
--- a/examples/rust/button/Cargo.lock
+++ b/examples/rust/button/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/button_abort/Cargo.lock b/examples/rust/button_abort/Cargo.lock
index 2e7de364..da3c8381 100644
--- a/examples/rust/button_abort/Cargo.lock
+++ b/examples/rust/button_abort/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/ccm/Cargo.lock b/examples/rust/ccm/Cargo.lock
index 1884c15b..0179315e 100644
--- a/examples/rust/ccm/Cargo.lock
+++ b/examples/rust/ccm/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/clock/Cargo.lock b/examples/rust/clock/Cargo.lock
index b4907753..e5b48865 100644
--- a/examples/rust/clock/Cargo.lock
+++ b/examples/rust/clock/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/ctap/Cargo.lock b/examples/rust/ctap/Cargo.lock
index dc4800a2..3840a5ad 100644
--- a/examples/rust/ctap/Cargo.lock
+++ b/examples/rust/ctap/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/ec_test/Cargo.lock b/examples/rust/ec_test/Cargo.lock
index 403a72eb..993fc4fe 100644
--- a/examples/rust/ec_test/Cargo.lock
+++ b/examples/rust/ec_test/Cargo.lock
@@ -302,6 +302,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "p256"
 version = "0.13.2"
@@ -539,6 +559,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -548,6 +569,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
@@ -572,6 +594,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-logger"
 version = "0.1.4-git"
@@ -593,6 +622,7 @@ dependencies = [
  "sha2",
  "signature",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
diff --git a/examples/rust/echo/Cargo.lock b/examples/rust/echo/Cargo.lock
index 10dd3a39..c18db1a6 100644
--- a/examples/rust/echo/Cargo.lock
+++ b/examples/rust/echo/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/client/Cargo.lock b/examples/rust/exercises/client/Cargo.lock
index b8e69e13..140f52b9 100644
--- a/examples/rust/exercises/client/Cargo.lock
+++ b/examples/rust/exercises/client/Cargo.lock
@@ -460,6 +460,26 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "p256"
 version = "0.13.2"
@@ -847,6 +867,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -856,6 +877,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -879,6 +901,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/interface/Cargo.lock b/examples/rust/exercises/interface/Cargo.lock
index 95c3dd86..7692723c 100644
--- a/examples/rust/exercises/interface/Cargo.lock
+++ b/examples/rust/exercises/interface/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -308,6 +328,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -317,6 +338,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -340,6 +362,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-1-sol/Cargo.lock b/examples/rust/exercises/part-1-sol/Cargo.lock
index ed02d58f..01aff399 100644
--- a/examples/rust/exercises/part-1-sol/Cargo.lock
+++ b/examples/rust/exercises/part-1-sol/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-1-sol"
 version = "0.1.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-1/Cargo.lock b/examples/rust/exercises/part-1/Cargo.lock
index b2c67d91..cae7cfc5 100644
--- a/examples/rust/exercises/part-1/Cargo.lock
+++ b/examples/rust/exercises/part-1/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-1"
 version = "0.1.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-2-sol/Cargo.lock b/examples/rust/exercises/part-2-sol/Cargo.lock
index e22c895e..518e4379 100644
--- a/examples/rust/exercises/part-2-sol/Cargo.lock
+++ b/examples/rust/exercises/part-2-sol/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-2-sol"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-2/Cargo.lock b/examples/rust/exercises/part-2/Cargo.lock
index 7642372f..f9e96a6c 100644
--- a/examples/rust/exercises/part-2/Cargo.lock
+++ b/examples/rust/exercises/part-2/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-2"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-3-sol/Cargo.lock b/examples/rust/exercises/part-3-sol/Cargo.lock
index f1e96859..8058fd29 100644
--- a/examples/rust/exercises/part-3-sol/Cargo.lock
+++ b/examples/rust/exercises/part-3-sol/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-3-sol"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-3/Cargo.lock b/examples/rust/exercises/part-3/Cargo.lock
index 7b6aa764..390857f5 100644
--- a/examples/rust/exercises/part-3/Cargo.lock
+++ b/examples/rust/exercises/part-3/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-3"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-4-sol/Cargo.lock b/examples/rust/exercises/part-4-sol/Cargo.lock
index c2a61940..9b3a578b 100644
--- a/examples/rust/exercises/part-4-sol/Cargo.lock
+++ b/examples/rust/exercises/part-4-sol/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-4-sol"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-4/Cargo.lock b/examples/rust/exercises/part-4/Cargo.lock
index 0f36ad81..2725559b 100644
--- a/examples/rust/exercises/part-4/Cargo.lock
+++ b/examples/rust/exercises/part-4/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-4"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-5-sol/Cargo.lock b/examples/rust/exercises/part-5-sol/Cargo.lock
index 56a22bb6..574c81be 100644
--- a/examples/rust/exercises/part-5-sol/Cargo.lock
+++ b/examples/rust/exercises/part-5-sol/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-5-sol"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-5/Cargo.lock b/examples/rust/exercises/part-5/Cargo.lock
index 40e1db33..51271f49 100644
--- a/examples/rust/exercises/part-5/Cargo.lock
+++ b/examples/rust/exercises/part-5/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-5"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-6-sol/Cargo.lock b/examples/rust/exercises/part-6-sol/Cargo.lock
index df3e3b4e..6c9d4923 100644
--- a/examples/rust/exercises/part-6-sol/Cargo.lock
+++ b/examples/rust/exercises/part-6-sol/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-6-sol"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-6/Cargo.lock b/examples/rust/exercises/part-6/Cargo.lock
index 7528c219..60a47827 100644
--- a/examples/rust/exercises/part-6/Cargo.lock
+++ b/examples/rust/exercises/part-6/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-6"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-7-sol/Cargo.lock b/examples/rust/exercises/part-7-sol/Cargo.lock
index 2e3e6260..ee67eea5 100644
--- a/examples/rust/exercises/part-7-sol/Cargo.lock
+++ b/examples/rust/exercises/part-7-sol/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-7-sol"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/exercises/part-7/Cargo.lock b/examples/rust/exercises/part-7/Cargo.lock
index c0026fe8..13d4e435 100644
--- a/examples/rust/exercises/part-7/Cargo.lock
+++ b/examples/rust/exercises/part-7/Cargo.lock
@@ -159,6 +159,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "part-7"
 version = "0.1.0"
@@ -316,6 +336,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -325,6 +346,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -348,6 +370,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/gcm_test/Cargo.lock b/examples/rust/gcm_test/Cargo.lock
index 97fc460f..d5d70ac4 100644
--- a/examples/rust/gcm_test/Cargo.lock
+++ b/examples/rust/gcm_test/Cargo.lock
@@ -176,6 +176,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -303,6 +323,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
  "zeroize",
 ]
@@ -313,6 +334,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -336,6 +358,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/gpio_test/Cargo.lock b/examples/rust/gpio_test/Cargo.lock
index 3c04d69b..c5941ba9 100644
--- a/examples/rust/gpio_test/Cargo.lock
+++ b/examples/rust/gpio_test/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/hash_test/Cargo.lock b/examples/rust/hash_test/Cargo.lock
index 13805e2c..18e36f08 100644
--- a/examples/rust/hash_test/Cargo.lock
+++ b/examples/rust/hash_test/Cargo.lock
@@ -313,6 +313,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "p256"
 version = "0.13.2"
@@ -553,6 +573,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
  "zeroize",
 ]
@@ -563,6 +584,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
@@ -587,6 +609,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-logger"
 version = "0.1.4-git"
@@ -608,6 +637,7 @@ dependencies = [
  "sha2",
  "signature",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-logger",
 ]
 
diff --git a/examples/rust/hello/Cargo.lock b/examples/rust/hello/Cargo.lock
index 94f4cd3d..86494bf9 100644
--- a/examples/rust/hello/Cargo.lock
+++ b/examples/rust/hello/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/hsm/Cargo.lock b/examples/rust/hsm/Cargo.lock
index c8bdd0f3..24096735 100644
--- a/examples/rust/hsm/Cargo.lock
+++ b/examples/rust/hsm/Cargo.lock
@@ -153,6 +153,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -271,6 +291,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -280,6 +301,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -303,6 +325,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/hsm/common/Cargo.lock b/examples/rust/hsm/common/Cargo.lock
index 5c475acc..12d3ab7c 100644
--- a/examples/rust/hsm/common/Cargo.lock
+++ b/examples/rust/hsm/common/Cargo.lock
@@ -146,6 +146,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -284,6 +304,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -293,6 +314,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -316,6 +338,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/hsm/common/src/lib.rs b/examples/rust/hsm/common/src/lib.rs
index 51eccc2c..2967a966 100644
--- a/examples/rust/hsm/common/src/lib.rs
+++ b/examples/rust/hsm/common/src/lib.rs
@@ -60,27 +60,6 @@ pub enum Error {
     UsbError,
 }
 
-#[cfg(feature = "api")]
-impl From<wasefire::crypto::Error> for Error {
-    fn from(_: wasefire::crypto::Error) -> Self {
-        Error::CryptoError
-    }
-}
-
-#[cfg(feature = "api")]
-impl From<wasefire::rng::Error> for Error {
-    fn from(_: wasefire::rng::Error) -> Self {
-        Error::RngError
-    }
-}
-
-#[cfg(feature = "api")]
-impl From<wasefire::store::Error> for Error {
-    fn from(_: wasefire::store::Error) -> Self {
-        Error::StoreError
-    }
-}
-
 pub trait Serializer {
     fn write_all(&mut self, data: &[u8]) -> Result<(), Error>;
     fn flush(&mut self) -> Result<(), Error>;
diff --git a/examples/rust/hsm/src/lib.rs b/examples/rust/hsm/src/lib.rs
index 9a180585..df73ec35 100644
--- a/examples/rust/hsm/src/lib.rs
+++ b/examples/rust/hsm/src/lib.rs
@@ -34,24 +34,26 @@ fn process(request: Request) -> Result<Response, Error> {
     match request {
         Request::GenerateKey { key } => {
             let mut secret = [0; 16];
-            rng::fill_bytes(&mut secret)?;
-            store::insert(key, &secret)?;
+            rng::fill_bytes(&mut secret).map_err(|_| Error::RngError)?;
+            store::insert(key, &secret).map_err(|_| Error::StoreError)?;
             Ok(Response::GenerateKey)
         }
         Request::DeleteKey { key } => {
-            store::remove(key)?;
+            store::remove(key).map_err(|_| Error::StoreError)?;
             Ok(Response::DeleteKey)
         }
         Request::Encrypt { key, nonce, data } => {
-            let data = crypto::ccm::encrypt(&find(key)?, &nonce, &data)?;
+            let data =
+                crypto::ccm::encrypt(&find(key)?, &nonce, &data).map_err(|_| Error::CryptoError)?;
             Ok(Response::Encrypt { data })
         }
         Request::Decrypt { key, nonce, data } => {
-            let data = crypto::ccm::decrypt(&find(key)?, &nonce, &data)?;
+            let data =
+                crypto::ccm::decrypt(&find(key)?, &nonce, &data).map_err(|_| Error::CryptoError)?;
             Ok(Response::Decrypt { data })
         }
         Request::ImportKey { key, secret } => {
-            store::insert(key, &secret)?;
+            store::insert(key, &secret).map_err(|_| Error::StoreError)?;
             Ok(Response::ImportKey)
         }
         Request::ExportKey { key } => Ok(Response::ExportKey { secret: find(key)? }),
@@ -60,7 +62,7 @@ fn process(request: Request) -> Result<Response, Error> {
 
 fn find(key: usize) -> Result<[u8; 16], Error> {
     let mut result = [0; 16];
-    let key = store::find(key)?.ok_or(Error::BadHandle)?;
+    let key = store::find(key).map_err(|_| Error::StoreError)?.ok_or(Error::BadHandle)?;
     if key.len() != result.len() {
         return Err(Error::BadHandle);
     }
diff --git a/examples/rust/led/Cargo.lock b/examples/rust/led/Cargo.lock
index 3011705b..b8ead145 100644
--- a/examples/rust/led/Cargo.lock
+++ b/examples/rust/led/Cargo.lock
@@ -145,6 +145,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/memory_game/Cargo.lock b/examples/rust/memory_game/Cargo.lock
index 922904f0..f8087b19 100644
--- a/examples/rust/memory_game/Cargo.lock
+++ b/examples/rust/memory_game/Cargo.lock
@@ -145,6 +145,26 @@ dependencies = [
  "wasefire",
 ]
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/oom/Cargo.lock b/examples/rust/oom/Cargo.lock
index 65741b77..e1d9f0c9 100644
--- a/examples/rust/oom/Cargo.lock
+++ b/examples/rust/oom/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "oom"
 version = "0.1.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/panic/Cargo.lock b/examples/rust/panic/Cargo.lock
index 08d57341..e77099d3 100644
--- a/examples/rust/panic/Cargo.lock
+++ b/examples/rust/panic/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "panic"
 version = "0.1.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/perf/Cargo.lock b/examples/rust/perf/Cargo.lock
index 645c9005..b55f5090 100644
--- a/examples/rust/perf/Cargo.lock
+++ b/examples/rust/perf/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "perf"
 version = "0.1.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/rand/Cargo.lock b/examples/rust/rand/Cargo.lock
index d84831c2..caabea88 100644
--- a/examples/rust/rand/Cargo.lock
+++ b/examples/rust/rand/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/reboot/Cargo.lock b/examples/rust/reboot/Cargo.lock
index 34845220..0aa501a8 100644
--- a/examples/rust/reboot/Cargo.lock
+++ b/examples/rust/reboot/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/rng_test/Cargo.lock b/examples/rust/rng_test/Cargo.lock
index 24e9a866..0c9d685c 100644
--- a/examples/rust/rng_test/Cargo.lock
+++ b/examples/rust/rng_test/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/store/Cargo.lock b/examples/rust/store/Cargo.lock
index 486821c1..be32e895 100644
--- a/examples/rust/store/Cargo.lock
+++ b/examples/rust/store/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/store/src/lib.rs b/examples/rust/store/src/lib.rs
index c4f55068..e9dab63f 100644
--- a/examples/rust/store/src/lib.rs
+++ b/examples/rust/store/src/lib.rs
@@ -80,7 +80,7 @@ impl<'a> Command<'a> {
         })
     }
 
-    fn process(&self) -> Result<(), store::Error> {
+    fn process(&self) -> Result<(), Error> {
         match self {
             Command::Insert { key, value } => insert(key, value.as_bytes()),
             Command::Find { key } => {
@@ -128,21 +128,21 @@ impl Key {
     }
 }
 
-fn insert(key: &Key, value: &[u8]) -> Result<(), store::Error> {
+fn insert(key: &Key, value: &[u8]) -> Result<(), Error> {
     match key {
         Key::Exact(key) => store::insert(*key, value),
         Key::Range(keys) => store::fragment::insert(keys.clone(), value),
     }
 }
 
-fn find(key: &Key) -> Result<Option<Box<[u8]>>, store::Error> {
+fn find(key: &Key) -> Result<Option<Box<[u8]>>, Error> {
     match key {
         Key::Exact(key) => store::find(*key),
         Key::Range(keys) => store::fragment::find(keys.clone()),
     }
 }
 
-fn remove(key: &Key) -> Result<(), store::Error> {
+fn remove(key: &Key) -> Result<(), Error> {
     match key {
         Key::Exact(key) => store::remove(*key),
         Key::Range(keys) => store::fragment::remove(keys.clone()),
diff --git a/examples/rust/store_test/Cargo.lock b/examples/rust/store_test/Cargo.lock
index 7c3c310b..8c87393e 100644
--- a/examples/rust/store_test/Cargo.lock
+++ b/examples/rust/store_test/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/sync_test/Cargo.lock b/examples/rust/sync_test/Cargo.lock
index 1c755ca6..8a87e671 100644
--- a/examples/rust/sync_test/Cargo.lock
+++ b/examples/rust/sync_test/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/syscall_test/Cargo.lock b/examples/rust/syscall_test/Cargo.lock
index d5e4c304..d08c3a72 100644
--- a/examples/rust/syscall_test/Cargo.lock
+++ b/examples/rust/syscall_test/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/syscall_test/src/lib.rs b/examples/rust/syscall_test/src/lib.rs
index f40c98f1..c4d6076d 100644
--- a/examples/rust/syscall_test/src/lib.rs
+++ b/examples/rust/syscall_test/src/lib.rs
@@ -18,6 +18,20 @@
 wasefire::applet!();
 
 fn main() {
-    debug::assert_eq(&syscall(1, 2, 3, 4), &5);
+    test_error();
     debug::exit(true);
 }
+
+fn test_error() {
+    debug!("test_error(): Check that errors are correctly converted.");
+    for (x, r) in [
+        (0, Ok(0)),
+        (0x7fffffff, Ok(0x7fffffff)),
+        (0xff000000, Err(Error::new(0xff, 0xffff))),
+        (0xfffefffd, Err(Error::user(2))),
+        (0xffffffff, Err(Error::default())),
+    ] {
+        debug!("- {x:08x} -> {r:?}");
+        debug::assert_eq(&Error::decode(syscall(0, 0, 0, x) as i32), &r);
+    }
+}
diff --git a/examples/rust/timer_test/Cargo.lock b/examples/rust/timer_test/Cargo.lock
index dc8ffa04..7804e178 100644
--- a/examples/rust/timer_test/Cargo.lock
+++ b/examples/rust/timer_test/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/update/Cargo.lock b/examples/rust/update/Cargo.lock
index 98a7ffe4..e051ffa2 100644
--- a/examples/rust/update/Cargo.lock
+++ b/examples/rust/update/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"
diff --git a/examples/rust/version/Cargo.lock b/examples/rust/version/Cargo.lock
index 86260b1a..7a0a16e7 100644
--- a/examples/rust/version/Cargo.lock
+++ b/examples/rust/version/Cargo.lock
@@ -138,6 +138,26 @@ version = "0.2.151"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
 
+[[package]]
+name = "num_enum"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683751d591e6d81200c39fb0d1032608b77724f34114db54f571ff1317b337c0"
+dependencies = [
+ "num_enum_derive",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c11e44798ad209ccdd91fc192f0526a369a01234f7373e1b141c96d7cee4f0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.41",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.6.0"
@@ -263,6 +283,7 @@ dependencies = [
  "sealed",
  "typenum",
  "wasefire-applet-api",
+ "wasefire-error",
  "wasefire-sync",
 ]
 
@@ -272,6 +293,7 @@ version = "0.6.0-git"
 dependencies = [
  "bytemuck",
  "wasefire-applet-api-macro",
+ "wasefire-error",
 ]
 
 [[package]]
@@ -295,6 +317,13 @@ dependencies = [
  "wasefire-applet-api-desc",
 ]
 
+[[package]]
+name = "wasefire-error"
+version = "0.1.0-git"
+dependencies = [
+ "num_enum",
+]
+
 [[package]]
 name = "wasefire-sync"
 version = "0.1.0-git"