diff --git a/reactos/dll/win32/msvcrt/msvcrt.def b/reactos/dll/win32/msvcrt/msvcrt.def
index bcf3fe378c8..a78d2cc87ef 100644
--- a/reactos/dll/win32/msvcrt/msvcrt.def
+++ b/reactos/dll/win32/msvcrt/msvcrt.def
@@ -852,6 +852,7 @@ EXPORTS
   _mbsnbcpy_s
   wcscpy_s
   wcsncpy_s
+  _wcsupr_s
   _ftol2=_ftol
   _ftol2_sse=_ftol
   strcat_s
diff --git a/reactos/lib/sdk/crt/string/wcs.c b/reactos/lib/sdk/crt/string/wcs.c
index 145fc9ce187..00941292911 100644
--- a/reactos/lib/sdk/crt/string/wcs.c
+++ b/reactos/lib/sdk/crt/string/wcs.c
@@ -109,6 +109,35 @@ wchar_t* CDECL _wcsset( wchar_t* str, wchar_t c )
   return ret;
 }
 
+/******************************************************************
+ *		_wcsupr_s (MSVCRT.@)
+ *
+ */
+INT CDECL _wcsupr_s( wchar_t* str, size_t n )
+{
+  wchar_t* ptr = str;
+
+  if (!str || !n)
+  {
+    if (str) *str = '\0';
+    __set_errno(EINVAL);
+    return EINVAL;
+  }
+
+  while (n--)
+  {
+    if (!*ptr) return 0;
+    *ptr = toupperW(*ptr);
+    ptr++;
+  }
+
+  /* MSDN claims that the function should return and set errno to
+   * ERANGE, which doesn't seem to be true based on the tests. */
+  *str = '\0';
+  __set_errno(EINVAL);
+  return EINVAL;
+}
+
 /*********************************************************************
  *		wcstod (MSVCRT.@)
  */