diff --git a/src/optimize/mod.rs b/src/optimize/mod.rs
index 7ce6daee205..33d75b36d96 100644
--- a/src/optimize/mod.rs
+++ b/src/optimize/mod.rs
@@ -5,7 +5,7 @@
 
 pub(crate) fn optimize_function<'tcx>(
     tcx: TyCtxt<'tcx>,
-    #[cfg_attr(not(debug_assertions), allow(unused_variables))] instance: Instance<'tcx>,
+    instance: Instance<'tcx>,
     ctx: &mut Context,
     cold_blocks: &EntitySet<Block>,
     clif_comments: &mut crate::pretty_clif::CommentWriter,