diff --git a/include/support/win32/locale_win32.h b/include/support/win32/locale_win32.h
index e035420f..019586c0 100644
--- a/include/support/win32/locale_win32.h
+++ b/include/support/win32/locale_win32.h
@@ -65,8 +65,21 @@ decltype(MB_CUR_MAX) MB_CUR_MAX_L( locale_t __l )
 #define strtoull_l _strtoui64_l
 // FIXME: current msvcrt does not know about long double
 #define strtold_l _strtod_l
-#define islower_l _islower_l
-#define isupper_l _isupper_l
+
+inline _LIBCPP_INLINE_VISIBILITY
+int
+islower_l(int c, _locale_t loc)
+{
+ return _islower_l((int)c, loc);
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+int
+isupper_l(int c, _locale_t loc)
+{
+ return _isupper_l((int)c, loc);
+}
+
 #define isdigit_l _isdigit_l
 #define isxdigit_l _isxdigit_l
 #define strcoll_l _strcoll_l