diff --git a/tests/ui/type-alias-impl-trait/issue-77179.rs b/tests/ui/type-alias-impl-trait/issue-77179.rs
index 093aeb4b27911..3d6c826d6ac5a 100644
--- a/tests/ui/type-alias-impl-trait/issue-77179.rs
+++ b/tests/ui/type-alias-impl-trait/issue-77179.rs
@@ -12,3 +12,8 @@ fn test() -> Pointer<_> {
 fn main() {
     test();
 }
+
+extern "Rust" {
+    fn bar() -> Pointer<_>;
+    //~^ ERROR: the placeholder `_` is not allowed within types
+}
diff --git a/tests/ui/type-alias-impl-trait/issue-77179.stderr b/tests/ui/type-alias-impl-trait/issue-77179.stderr
index 68dd6570d00c0..c5cacfd3cd351 100644
--- a/tests/ui/type-alias-impl-trait/issue-77179.stderr
+++ b/tests/ui/type-alias-impl-trait/issue-77179.stderr
@@ -7,6 +7,15 @@ LL | fn test() -> Pointer<_> {
    |              |       not allowed in type signatures
    |              help: replace with the correct return type: `Pointer<i32>`
 
-error: aborting due to 1 previous error
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for functions
+  --> $DIR/issue-77179.rs:17:25
+   |
+LL |     fn bar() -> Pointer<_>;
+   |                         ^
+   |                         |
+   |                         not allowed in type signatures
+   |                         help: use type parameters instead: `T`
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0121`.