diff --git a/llvm/lib/Support/Regex.cpp b/llvm/lib/Support/Regex.cpp
--- a/llvm/lib/Support/Regex.cpp
+++ b/llvm/lib/Support/Regex.cpp
@@ -14,14 +14,11 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "regex_impl.h"
+
 #include <cassert>
 #include <string>
 
-// Important this comes last because it defines "_REGEX_H_". At least on
-// Darwin, if included before any header that (transitively) includes
-// xlocale.h, this will cause trouble, because of missing regex-related types.
-#include "regex_impl.h"
-
 using namespace llvm;
 
 Regex::Regex() : preg(nullptr), error(REG_BADPAT) {}