diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs
index 3e4c67c4d1f..e03e24e606d 100644
--- a/src/libcore/cell.rs
+++ b/src/libcore/cell.rs
@@ -482,6 +482,7 @@ mod test {
     }
 
     #[test]
+    #[allow(experimental)]
     fn clone_ref_updates_flag() {
         let x = RefCell::new(0);
         {