diff --git a/clang/lib/Headers/stddef.h b/clang/lib/Headers/stddef.h
index 52962248f67f..a8d6bf414886 100644
--- a/clang/lib/Headers/stddef.h
+++ b/clang/lib/Headers/stddef.h
@@ -53,7 +53,9 @@ typedef __WCHAR_TYPE__ wchar_t;
 #endif
 
 #undef NULL
-#ifdef __cplusplus
+#if defined(__APPLE__) && defined(__DARWIN_NULL)
+#  define NULL __DARWIN_NULL
+#elif defined(__cplusplus)
 #  if !defined(__MINGW32__) && !defined(_MSC_VER)
 #    define NULL __null
 #  else