diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 5d6e7dcfcee87..e2a2428fbc244 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -851,6 +851,8 @@ impl<T> [T] {
 
     /// Swaps two elements in the slice.
     ///
+    /// If `a` equals to `b`, it's guaranteed that elements won't change value.
+    ///
     /// # Arguments
     ///
     /// * a - The index of the first element