diff --git a/llvm/include/llvm/ADT/StringRef.h b/llvm/include/llvm/ADT/StringRef.h
--- a/llvm/include/llvm/ADT/StringRef.h
+++ b/llvm/include/llvm/ADT/StringRef.h
@@ -78,11 +78,11 @@
 
     // Constexpr version of std::strlen.
     static constexpr size_t strLen(const char *Str) {
-#if __cplusplus > 201402L
-      return std::char_traits<char>::length(Str);
-#elif __has_builtin(__builtin_strlen) || defined(__GNUC__) || \
+#if __has_builtin(__builtin_strlen) || defined(__GNUC__) || \
     (defined(_MSC_VER) && _MSC_VER >= 1916)
       return __builtin_strlen(Str);
+#elif __cplusplus > 201402L && !defined(_MSC_VER)
+      return std::char_traits<char>::length(Str);
 #else
       const char *Begin = Str;
       while (*Str != '\0')