diff --git a/include/memory b/include/memory
index 69702c6..26ba564 100644
--- a/include/memory
+++ b/include/memory
@@ -1787,6 +1787,7 @@
     typedef const _Tp         value_type;
 
     typedef true_type propagate_on_container_move_assignment;
+    typedef true_type is_always_equal;
 
     template <class _Up> struct rebind {typedef allocator<_Up> other;};