diff --git a/crates/typescript-tests/src/opt_args_and_ret.rs b/crates/typescript-tests/src/opt_args_and_ret.rs
index e960826befa..024bfe3cb09 100644
--- a/crates/typescript-tests/src/opt_args_and_ret.rs
+++ b/crates/typescript-tests/src/opt_args_and_ret.rs
@@ -1,6 +1,14 @@
 use wasm_bindgen::prelude::*;
 
 #[wasm_bindgen]
-pub fn opt_fn(_a: Option<i32>) -> Option<i32> {
+/// Optional parameters followed by non-optional parameters.
+/// Only the parameter _c may be marked as omittable.
+pub fn opt_fn_mixed(_a: Option<i32>, _b: i32, _c: Option<i32>) -> Option<i32> {
+    None
+}
+
+#[wasm_bindgen]
+/// Only optional parameters. All of them may be marked as omittable.
+pub fn opt_fn_only(_a: Option<i32>, _b: Option<i32>, _c: Option<i32>) -> Option<i32> {
     None
 }
diff --git a/crates/typescript-tests/src/opt_args_and_ret.ts b/crates/typescript-tests/src/opt_args_and_ret.ts
index 85a76696d7c..10fe60508cc 100644
--- a/crates/typescript-tests/src/opt_args_and_ret.ts
+++ b/crates/typescript-tests/src/opt_args_and_ret.ts
@@ -1,3 +1,4 @@
 import * as wbg from '../pkg/typescript_tests';
 
-const opt_fn: (a?: number) => number | undefined = wbg.opt_fn;
+const opt_fn_mixed: (a: number | undefined, b: number, c?: number) => number | undefined = wbg.opt_fn_mixed;
+const opt_fn_only: (a?: number, b?: number, c?: number) => number | undefined = wbg.opt_fn_only;