diff --git a/alloc_miri_test/Cargo.toml b/alloc_miri_test/Cargo.toml
index 7c7eb2e..8195800 100644
--- a/alloc_miri_test/Cargo.toml
+++ b/alloc_miri_test/Cargo.toml
@@ -10,6 +10,12 @@ edition = "2018"
 name = "alloc_miri_test"
 path = "../liballoc/src/lib.rs"
 
+[features]
+# Empty this crate to avoid two copies of liballoc.
+# See https://github.com/rust-lang/miri-test-libstd/issues/4.
+default = ["miri-test-libstd"]
+miri-test-libstd = []
+
 [dependencies]
 
 [dev-dependencies]
diff --git a/core_miri_test/Cargo.toml b/core_miri_test/Cargo.toml
index 524cce8..e25c244 100644
--- a/core_miri_test/Cargo.toml
+++ b/core_miri_test/Cargo.toml
@@ -12,6 +12,12 @@ path = "../libcore/src/lib.rs"
 test = false
 bench = false
 
+[features]
+# Empty this crate to avoid two copies of libcore.
+# See https://github.com/rust-lang/miri-test-libstd/issues/4.
+default = ["miri-test-libstd"]
+miri-test-libstd = []
+
 [[test]]
 name = "coretests"
 path = "../libcore/tests/lib.rs"
diff --git a/rust-version b/rust-version
index 7948996..2e83157 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-nightly-2021-07-09
+nightly-2021-07-24