diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index e72b6117ba86..e16a428feb64 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -1134,6 +1134,7 @@ mod impls {
                 -1 => Less,
                 0 => Equal,
                 1 => Greater,
+                // SAFETY: Unreachable code
                 _ => unsafe { unreachable_unchecked() },
             }
         }