diff --git a/build/secondary/third_party/libcxx/config/__config_site b/build/secondary/third_party/libcxx/config/__config_site
index 106c24fc3613b..e1a46ff65e409 100644
--- a/build/secondary/third_party/libcxx/config/__config_site
+++ b/build/secondary/third_party/libcxx/config/__config_site
@@ -1,8 +1,9 @@
 #ifndef _LIBCPP_CONFIG_SITE
 #define _LIBCPP_CONFIG_SITE
 
-/* #undef _LIBCPP_ABI_VERSION */
-/* #undef _LIBCPP_ABI_UNSTABLE */
+#define _LIBCPP_ABI_VERSION 1
+#define _LIBCPP_ABI_NAMESPACE _fl
+
 /* #undef _LIBCPP_ABI_FORCE_ITANIUM */
 /* #undef _LIBCPP_ABI_FORCE_MICROSOFT */
 /* #undef _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT */