diff --git a/include/__config b/include/__config
index ca850d39..f003e5b0 100644
--- a/include/__config
+++ b/include/__config
@@ -518,6 +518,13 @@ template <unsigned> struct __static_assert_check {};
 #  endif
 #endif  // _LIBCPP_STD_VER
 
+#if _LIBCPP_STD_VER <= 11
+#define _LIBCPP_CONSTEXPR_AFTER_CXX11
+#else
+#define _LIBCPP_CONSTEXPR_AFTER_CXX11 constexpr
+#endif
+
+
 #ifdef _LIBCPP_DEBUG2
 #   include <__debug>
 #else