diff --git a/dlls/msvcrt/file.c b/dlls/msvcrt/file.c
index d5c227190c0..d20fa8e6a23 100644
--- a/dlls/msvcrt/file.c
+++ b/dlls/msvcrt/file.c
@@ -3179,8 +3179,8 @@ int CDECL MSVCRT__wstat64(const MSVCRT_wchar_t* path, struct MSVCRT__stat64 * bu
     /* executable? */
     if (plen > 6 && path[plen-4] == '.')  /* shortest exe: "\x.exe" */
     {
-      ULONGLONG ext = tolowerW(path[plen-1]) | (tolowerW(path[plen-2]) << 16) |
-                               ((ULONGLONG)tolowerW(path[plen-3]) << 32);
+      ULONGLONG ext = MSVCRT_towlower(path[plen-1]) | (MSVCRT_towlower(path[plen-2]) << 16) |
+                               ((ULONGLONG)MSVCRT_towlower(path[plen-3]) << 32);
       if (ext == WCEXE || ext == WCBAT || ext == WCCMD || ext == WCCOM)
         mode |= ALL_S_IEXEC;
     }
diff --git a/dlls/msvcrt/msvcrt.h b/dlls/msvcrt/msvcrt.h
index cc4541cceef..7c92abc4fda 100644
--- a/dlls/msvcrt/msvcrt.h
+++ b/dlls/msvcrt/msvcrt.h
@@ -1199,6 +1199,7 @@ char* __cdecl MSVCRT__itoa(int, char*, int);
 double parse_double(MSVCRT_wchar_t (*)(void*), void (*)(void*), void*, MSVCRT_pthreadlocinfo, int*);
 int __cdecl MSVCRT_wcsncmp(const MSVCRT_wchar_t*, const MSVCRT_wchar_t*, MSVCRT_size_t);
 int __cdecl MSVCRT__wcsnicmp(const MSVCRT_wchar_t*, const MSVCRT_wchar_t*, MSVCRT_size_t);
+int __cdecl MSVCRT_towlower(MSVCRT_wint_t);
 
 /* Maybe one day we'll enable the invalid parameter handlers with the full set of information (msvcrXXd)
  *      #define MSVCRT_INVALID_PMT(x) MSVCRT_call_invalid_parameter_handler(x, __FUNCTION__, __FILE__, __LINE__, 0)
diff --git a/dlls/msvcrt/wcs.c b/dlls/msvcrt/wcs.c
index f715832c264..ec59990496d 100644
--- a/dlls/msvcrt/wcs.c
+++ b/dlls/msvcrt/wcs.c
@@ -411,7 +411,7 @@ int CDECL MSVCRT__wcslwr_s_l( MSVCRT_wchar_t* str, MSVCRT_size_t n, MSVCRT__loca
   while (n--)
   {
     if (!*ptr) return 0;
-    *ptr = tolowerW(*ptr);
+    *ptr = MSVCRT__towlower_l(*ptr, locale);
     ptr++;
   }
 
@@ -2345,7 +2345,7 @@ __int64 CDECL MSVCRT__wcstoi64_l(const MSVCRT_wchar_t *nptr,
     } else if(*nptr == '+')
         nptr++;
 
-    if((base==0 || base==16) && wctoint(*nptr, 1)==0 && tolowerW(*(nptr+1))=='x') {
+    if((base==0 || base==16) && wctoint(*nptr, 1)==0 && (nptr[1]=='x' || nptr[1]=='X')) {
         base = 16;
         nptr += 2;
     }
@@ -2518,7 +2518,7 @@ unsigned __int64 CDECL MSVCRT__wcstoui64_l(const MSVCRT_wchar_t *nptr,
     } else if(*nptr == '+')
         nptr++;
 
-    if((base==0 || base==16) && wctoint(*nptr, 1)==0 && tolowerW(*(nptr+1))=='x') {
+    if((base==0 || base==16) && wctoint(*nptr, 1)==0 && (nptr[1]=='x' || nptr[1]=='X')) {
         base = 16;
         nptr += 2;
     }