diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index 64e37ec5a56c..72ff9cca9fd8 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -96,6 +96,7 @@ use self::Ordering::*;
 /// For example, let's tweak our previous code a bit:
 ///
 /// ```
+/// // The derive implements <BookFormat> == <BookFormat> comparisons
 /// #[derive(PartialEq)]
 /// enum BookFormat {
 ///     Paperback,