diff --git a/src/test/ui/extern/extern-compare-with-return-type.rs b/src/test/ui/extern/extern-compare-with-return-type.rs
index 6c9ed3760f6e4..52b51bb943aa6 100644
--- a/src/test/ui/extern/extern-compare-with-return-type.rs
+++ b/src/test/ui/extern/extern-compare-with-return-type.rs
@@ -2,8 +2,9 @@
 // Tests that we can compare various kinds of extern fn signatures.
 #![allow(non_camel_case_types)]
 
-extern fn voidret1() {}
-extern fn voidret2() {}
+// `dbg!()` differentiates these functions to ensure they won't be merged.
+extern fn voidret1() { dbg!() }
+extern fn voidret2() { dbg!() }
 
 extern fn uintret() -> usize { 22 }