diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index 6f4c130d8f31..01db55a00f64 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -1541,6 +1541,10 @@ impl<T> [T] {
     /// let src = [1, 2, 3, 4];
     /// let mut dst = [0, 0];
     ///
+    /// // Note: the slices must be the same length, so
+    /// // you can slice the source to be the same size.
+    /// // Here we slice the source, four elements, to two, the same size
+    /// // as the destination slice. It *will* panic if we don't do this.
     /// dst.clone_from_slice(&src[2..]);
     ///
     /// assert_eq!(src, [1, 2, 3, 4]);
@@ -1607,6 +1611,10 @@ impl<T> [T] {
     /// let src = [1, 2, 3, 4];
     /// let mut dst = [0, 0];
     ///
+    /// // Note: the slices must be the same length, so
+    /// // you can slice the source to be the same size.
+    /// // Here we slice the source, four elements, to two, the same size
+    /// // as the destination slice. It *will* panic if we don't do this.
     /// dst.copy_from_slice(&src[2..]);
     ///
     /// assert_eq!(src, [1, 2, 3, 4]);