diff --git a/dlls/api-ms-win-crt-convert-l1-1-0/api-ms-win-crt-convert-l1-1-0.spec b/dlls/api-ms-win-crt-convert-l1-1-0/api-ms-win-crt-convert-l1-1-0.spec
index f5b77d6a99c..c0e287321a9 100644
--- a/dlls/api-ms-win-crt-convert-l1-1-0/api-ms-win-crt-convert-l1-1-0.spec
+++ b/dlls/api-ms-win-crt-convert-l1-1-0/api-ms-win-crt-convert-l1-1-0.spec
@@ -102,7 +102,7 @@
 @ cdecl -ret64 strtoull(str ptr long) ucrtbase.strtoull
 @ cdecl -ret64 strtoumax(str ptr long) ucrtbase.strtoumax
 @ cdecl wcrtomb(ptr long ptr) ucrtbase.wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) ucrtbase.wcrtomb_s
 @ cdecl wcsrtombs(ptr ptr long ptr) ucrtbase.wcsrtombs
 @ cdecl wcsrtombs_s(ptr ptr long ptr long ptr) ucrtbase.wcsrtombs_s
 @ cdecl wcstod(wstr ptr) ucrtbase.wcstod
diff --git a/dlls/msvcr100/msvcr100.spec b/dlls/msvcr100/msvcr100.spec
index cf4d6d4cd29..895298478d7 100644
--- a/dlls/msvcr100/msvcr100.spec
+++ b/dlls/msvcr100/msvcr100.spec
@@ -1853,7 +1853,7 @@
 @ cdecl vwprintf(wstr ptr) MSVCRT_vwprintf
 @ cdecl vwprintf_s(wstr ptr) MSVCRT_vwprintf_s
 @ cdecl wcrtomb(ptr long ptr) MSVCRT_wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) MSVCRT_wcrtomb_s
 @ cdecl wcscat(wstr wstr) ntdll.wcscat
 @ cdecl wcscat_s(wstr long wstr) MSVCRT_wcscat_s
 @ cdecl wcschr(wstr long) MSVCRT_wcschr
diff --git a/dlls/msvcr110/msvcr110.spec b/dlls/msvcr110/msvcr110.spec
index 410aae44768..66c6f65a9b9 100644
--- a/dlls/msvcr110/msvcr110.spec
+++ b/dlls/msvcr110/msvcr110.spec
@@ -2211,7 +2211,7 @@
 @ cdecl vwprintf(wstr ptr) MSVCRT_vwprintf
 @ cdecl vwprintf_s(wstr ptr) MSVCRT_vwprintf_s
 @ cdecl wcrtomb(ptr long ptr) MSVCRT_wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) MSVCRT_wcrtomb_s
 @ cdecl wcscat(wstr wstr) ntdll.wcscat
 @ cdecl wcscat_s(wstr long wstr) MSVCRT_wcscat_s
 @ cdecl wcschr(wstr long) MSVCRT_wcschr
diff --git a/dlls/msvcr120/msvcr120.spec b/dlls/msvcr120/msvcr120.spec
index 171cfd27e18..8c9d93fd81b 100644
--- a/dlls/msvcr120/msvcr120.spec
+++ b/dlls/msvcr120/msvcr120.spec
@@ -2446,7 +2446,7 @@
 @ stub vwscanf
 @ stub vwscanf_s
 @ cdecl wcrtomb(ptr long ptr) MSVCRT_wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) MSVCRT_wcrtomb_s
 @ cdecl wcscat(wstr wstr) ntdll.wcscat
 @ cdecl wcscat_s(wstr long wstr) MSVCRT_wcscat_s
 @ cdecl wcschr(wstr long) MSVCRT_wcschr
diff --git a/dlls/msvcr120_app/msvcr120_app.spec b/dlls/msvcr120_app/msvcr120_app.spec
index f9e3a0087f4..ba1b351e899 100644
--- a/dlls/msvcr120_app/msvcr120_app.spec
+++ b/dlls/msvcr120_app/msvcr120_app.spec
@@ -2108,7 +2108,7 @@
 @ stub vwscanf
 @ stub vwscanf_s
 @ cdecl wcrtomb(ptr long ptr) msvcr120.wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) msvcr120.wcrtomb_s
 @ cdecl wcscat(wstr wstr) msvcr120.wcscat
 @ cdecl wcscat_s(wstr long wstr) msvcr120.wcscat_s
 @ cdecl wcschr(wstr long) msvcr120.wcschr
diff --git a/dlls/msvcr80/msvcr80.spec b/dlls/msvcr80/msvcr80.spec
index 3fc18d2c8d1..f8d0920c3c9 100644
--- a/dlls/msvcr80/msvcr80.spec
+++ b/dlls/msvcr80/msvcr80.spec
@@ -1533,7 +1533,7 @@
 @ cdecl vwprintf(wstr ptr) MSVCRT_vwprintf
 @ cdecl vwprintf_s(wstr ptr) MSVCRT_vwprintf_s
 @ cdecl wcrtomb(ptr long ptr) MSVCRT_wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) MSVCRT_wcrtomb_s
 @ cdecl wcscat(wstr wstr) ntdll.wcscat
 @ cdecl wcscat_s(wstr long wstr) MSVCRT_wcscat_s
 @ cdecl wcschr(wstr long) MSVCRT_wcschr
diff --git a/dlls/msvcr90/msvcr90.spec b/dlls/msvcr90/msvcr90.spec
index 4050f423823..d2f469a77dc 100644
--- a/dlls/msvcr90/msvcr90.spec
+++ b/dlls/msvcr90/msvcr90.spec
@@ -1506,7 +1506,7 @@
 @ cdecl vwprintf(wstr ptr) MSVCRT_vwprintf
 @ cdecl vwprintf_s(wstr ptr) MSVCRT_vwprintf_s
 @ cdecl wcrtomb(ptr long ptr) MSVCRT_wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) MSVCRT_wcrtomb_s
 @ cdecl wcscat(wstr wstr) ntdll.wcscat
 @ cdecl wcscat_s(wstr long wstr) MSVCRT_wcscat_s
 @ cdecl wcschr(wstr long) MSVCRT_wcschr
diff --git a/dlls/msvcrt/msvcrt.spec b/dlls/msvcrt/msvcrt.spec
index e6f0841f7f6..9f2a70c2f9d 100644
--- a/dlls/msvcrt/msvcrt.spec
+++ b/dlls/msvcrt/msvcrt.spec
@@ -1480,7 +1480,7 @@
 @ cdecl vwprintf(wstr ptr) MSVCRT_vwprintf
 @ cdecl vwprintf_s(wstr ptr) MSVCRT_vwprintf_s
 @ cdecl wcrtomb(ptr long ptr) MSVCRT_wcrtomb
-# stub wcrtomb_s(ptr ptr long long ptr)
+@ cdecl wcrtomb_s(ptr ptr long long ptr) MSVCRT_wcrtomb_s
 @ cdecl wcscat(wstr wstr) ntdll.wcscat
 @ cdecl wcscat_s(wstr long wstr) MSVCRT_wcscat_s
 @ cdecl wcschr(wstr long) MSVCRT_wcschr
diff --git a/dlls/msvcrt/wcs.c b/dlls/msvcrt/wcs.c
index 6b8c7bbe0f3..f84963ce2e3 100644
--- a/dlls/msvcrt/wcs.c
+++ b/dlls/msvcrt/wcs.c
@@ -1821,6 +1821,20 @@ INT CDECL MSVCRT_wctob( MSVCRT_wint_t wchar )
     return MSVCRT_EOF;
 }
 
+/*********************************************************************
+ *              wcrtomb_s (MSVCRT.@)
+ */
+INT CDECL MSVCRT_wcrtomb_s(MSVCRT_size_t *len, char *mbchar,
+        MSVCRT_size_t size, MSVCRT_wchar_t wch, MSVCRT_mbstate_t *s)
+{
+    int ilen, ret;
+
+    if (s) *s = 0;
+    ret = MSVCRT_wctomb_s(&ilen, mbchar, size, wch);
+    if (len) *len = ilen;
+    return ret;
+}
+
 /*********************************************************************
  *              wcrtomb (MSVCRT.@)
  */
diff --git a/dlls/ucrtbase/ucrtbase.spec b/dlls/ucrtbase/ucrtbase.spec
index 6b7a140b199..3b590ee2660 100644
--- a/dlls/ucrtbase/ucrtbase.spec
+++ b/dlls/ucrtbase/ucrtbase.spec
@@ -2553,7 +2553,7 @@
 @ cdecl ungetc(long ptr) MSVCRT_ungetc
 @ cdecl ungetwc(long ptr) MSVCRT_ungetwc
 @ cdecl wcrtomb(ptr long ptr) MSVCRT_wcrtomb
-@ stub wcrtomb_s
+@ cdecl wcrtomb_s(ptr ptr long long ptr) MSVCRT_wcrtomb_s
 @ cdecl wcscat(wstr wstr) ntdll.wcscat
 @ cdecl wcscat_s(wstr long wstr) MSVCRT_wcscat_s
 @ cdecl wcschr(wstr long) MSVCRT_wcschr