diff --git a/tests/ui/crashes/ice-4968.rs b/tests/ui/crashes/ice-4968.rs
index a584dd61780..3822f174598 100644
--- a/tests/ui/crashes/ice-4968.rs
+++ b/tests/ui/crashes/ice-4968.rs
@@ -2,6 +2,8 @@
 
 // Test for https://github.com/rust-lang/rust-clippy/issues/4968
 
+#![warn(clippy::unsound_collection_transmute)]
+
 trait Trait {
     type Assoc;
 }