diff --git a/dlls/msvcr80/msvcr80.spec b/dlls/msvcr80/msvcr80.spec
index 6ead0a77f42..3866dc65ccb 100644
--- a/dlls/msvcr80/msvcr80.spec
+++ b/dlls/msvcr80/msvcr80.spec
@@ -1110,7 +1110,7 @@
 @ cdecl _wcstoi64_l(wstr ptr long ptr) msvcrt._wcstoi64_l
 @ stub _wcstol_l
 @ stub _wcstombs_l
-@ stub _wcstombs_s_l
+@ cdecl _wcstombs_s_l(ptr ptr long wstr long ptr) msvcrt._wcstombs_s_l
 @ cdecl _wcstoui64(wstr ptr long) msvcrt._wcstoui64
 @ cdecl _wcstoui64_l(wstr ptr long ptr) msvcrt._wcstoui64_l
 @ stub _wcstoul_l
@@ -1456,7 +1456,7 @@
 @ stub wcstok_s
 @ cdecl wcstol(wstr ptr long) msvcrt.wcstol
 @ cdecl wcstombs(ptr ptr long) msvcrt.wcstombs
-@ stub wcstombs_s
+@ cdecl wcstombs_s(ptr ptr long wstr long) msvcrt.wcstombs_s
 @ cdecl wcstoul(wstr ptr long) msvcrt.wcstoul
 @ stub wcsxfrm
 @ stub wctob
diff --git a/dlls/msvcr90/msvcr90.spec b/dlls/msvcr90/msvcr90.spec
index 72dff798245..ea3e534eb8d 100644
--- a/dlls/msvcr90/msvcr90.spec
+++ b/dlls/msvcr90/msvcr90.spec
@@ -1097,7 +1097,7 @@
 @ cdecl _wcstoi64_l(wstr ptr long ptr) msvcrt._wcstoi64_l
 @ stub _wcstol_l
 @ stub _wcstombs_l
-@ stub _wcstombs_s_l
+@ cdecl _wcstombs_s_l(ptr ptr long wstr long ptr) msvcrt._wcstombs_s_l
 @ cdecl _wcstoui64(wstr ptr long) msvcrt._wcstoui64
 @ cdecl _wcstoui64_l(wstr ptr long ptr) msvcrt._wcstoui64_l
 @ stub _wcstoul_l
@@ -1440,7 +1440,7 @@
 @ stub wcstok_s
 @ cdecl wcstol(wstr ptr long) msvcrt.wcstol
 @ cdecl wcstombs(ptr ptr long) msvcrt.wcstombs
-@ stub wcstombs_s
+@ cdecl wcstombs_s(ptr ptr long wstr long) msvcrt.wcstombs_s
 @ cdecl wcstoul(wstr ptr long) msvcrt.wcstoul
 @ stub wcsxfrm
 @ stub wctob
diff --git a/dlls/msvcrt/msvcrt.spec b/dlls/msvcrt/msvcrt.spec
index 5f82cf1b9e2..1e7b9e20643 100644
--- a/dlls/msvcrt/msvcrt.spec
+++ b/dlls/msvcrt/msvcrt.spec
@@ -1039,7 +1039,7 @@
 @ cdecl _wcstoi64_l(wstr ptr long ptr) MSVCRT__wcstoi64_l
 # stub _wcstol_l
 # stub _wcstombs_l
-# stub _wcstombs_s_l
+@ cdecl _wcstombs_s_l(ptr ptr long wstr long ptr) MSVCRT__wcstombs_s_l
 @ cdecl _wcstoui64(wstr ptr long) MSVCRT__wcstoui64
 @ cdecl _wcstoui64_l(wstr ptr long ptr) MSVCRT__wcstoui64_l
 # stub _wcstoul_l
@@ -1396,7 +1396,7 @@
 # stub wcstok_s
 @ cdecl wcstol(wstr ptr long) ntdll.wcstol
 @ cdecl wcstombs(ptr ptr long) ntdll.wcstombs
-# stub wcstombs_s
+@ cdecl wcstombs_s(ptr ptr long wstr long) MSVCRT_wcstombs_s
 @ cdecl wcstoul(wstr ptr long) ntdll.wcstoul
 @ stub wcsxfrm #(ptr wstr long) MSVCRT_wcsxfrm
 # stub wctob
diff --git a/dlls/msvcrt/wcs.c b/dlls/msvcrt/wcs.c
index 04d90dea4b6..ddeb9997205 100644
--- a/dlls/msvcrt/wcs.c
+++ b/dlls/msvcrt/wcs.c
@@ -226,6 +226,82 @@ double CDECL MSVCRT__wcstod_l(const MSVCRT_wchar_t* str, MSVCRT_wchar_t** end,
     return ret;
 }
 
+/*********************************************************************
+ *		_wcstombs_s_l (MSVCRT.@)
+ */
+int CDECL MSVCRT__wcstombs_s_l(MSVCRT_size_t *ret, char *mbstr,
+        MSVCRT_size_t size, const MSVCRT_wchar_t *wcstr,
+        MSVCRT_size_t count, MSVCRT__locale_t locale)
+{
+    char default_char = '\0', *p;
+    int hlp, len;
+
+    if(!size)
+        return 0;
+
+    if(!mbstr || !wcstr) {
+        MSVCRT__invalid_parameter(NULL, NULL, NULL, 0, 0);
+        if(mbstr)
+            *mbstr = '\0';
+        *MSVCRT__errno() = MSVCRT_EINVAL;
+        return MSVCRT_EINVAL;
+    }
+
+    if(!locale)
+        locale = get_locale();
+
+    if(size<=count)
+        len = size;
+    else if(count==_TRUNCATE)
+        len = size-1;
+    else
+        len = count;
+
+    p = mbstr;
+    *ret = 0;
+    while(1) {
+        if(!len)
+            break;
+
+        if(*wcstr == '\0') {
+            *p = '\0';
+            break;
+        }
+
+        hlp = WideCharToMultiByte(locale->locinfo->lc_codepage,
+                WC_NO_BEST_FIT_CHARS, wcstr, 1, p, len, &default_char, NULL);
+        if(!hlp || *p=='\0')
+            break;
+
+        p += hlp;
+        len -= hlp;
+
+        wcstr++;
+        *ret += 1;
+    }
+
+    if(!len && size<=count) {
+        MSVCRT__invalid_parameter(NULL, NULL, NULL, 0, 0);
+        *mbstr = '\0';
+        *MSVCRT__errno() = MSVCRT_ERANGE;
+        return MSVCRT_ERANGE;
+    }
+
+    if(*wcstr == '\0')
+        *ret += 1;
+    *p = '\0';
+    return 0;
+}
+
+/*********************************************************************
+ *		wcstombs_s (MSVCRT.@)
+ */
+int CDECL MSVCRT_wcstombs_s(MSVCRT_size_t *ret, char *mbstr,
+        MSVCRT_size_t size, const MSVCRT_wchar_t *wcstr, MSVCRT_size_t count)
+{
+    return MSVCRT__wcstombs_s_l(ret, mbstr, size, wcstr, count, NULL);
+}
+
 /*********************************************************************
  *		wcstod (MSVCRT.@)
  */