diff --git a/src/libcollections/btree/node.rs b/src/libcollections/btree/node.rs
index d36fe669fa37..e0018efe9e0d 100644
--- a/src/libcollections/btree/node.rs
+++ b/src/libcollections/btree/node.rs
@@ -390,7 +390,7 @@ impl<K, V> Node<K, V> {
 
     #[inline]
     pub fn as_slices_internal_mut<'b>(&'b mut self) -> MutNodeSlice<'b, K, V> {
-        // TODO: Bad: This relies on structure layout!
+        // FIXME(#27620): Bad: This relies on structure layout!
         unsafe { mem::transmute(self.as_slices_internal()) }
     }