diff --git a/src/libcore/iter/adapters/mod.rs b/src/libcore/iter/adapters/mod.rs
index 6eb837ed0fed8..1243aefcc1ea9 100644
--- a/src/libcore/iter/adapters/mod.rs
+++ b/src/libcore/iter/adapters/mod.rs
@@ -504,6 +504,9 @@ where
 #[stable(feature = "fused", since = "1.26.0")]
 impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<I> TrustedLen for Cycle<I> where I: Clone + TrustedLen {}
+
 /// An iterator for stepping iterators by a custom amount.
 ///
 /// This `struct` is created by the [`step_by`] method on [`Iterator`]. See