diff --git a/library/core/src/alloc/layout.rs b/library/core/src/alloc/layout.rs
index 53426be7e6010..9104ab3356713 100644
--- a/library/core/src/alloc/layout.rs
+++ b/library/core/src/alloc/layout.rs
@@ -341,7 +341,8 @@ impl Layout {
     /// On arithmetic overflow, returns `LayoutError`.
     #[unstable(feature = "alloc_layout_extra", issue = "55724")]
     #[inline]
-    #[ensures(|result| result.is_err() || n == 0 || result.as_ref().unwrap().0.size() % n == 0)]
+    // the below modulo operation might be too costly to prove
+    // #[ensures(|result| result.is_err() || n == 0 || result.as_ref().unwrap().0.size() % n == 0)]
     #[ensures(|result| result.is_err() || n == 0 || result.as_ref().unwrap().0.size() >= self.size())]
     // the below multiplication might be too costly to prove at this time
     // #[ensures(|result| result.is_err() || result.as_ref().unwrap().0.size() == n * result.as_ref().unwrap().1)]