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 b38905b134d..e2b5ab9877b 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
@@ -88,7 +88,7 @@
 @ stub mbrtoc32
 @ cdecl mbrtowc(ptr str long ptr) ucrtbase.mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) ucrtbase.mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) ucrtbase.mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) ucrtbase.mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) ucrtbase.mbstowcs_s
 @ cdecl mbtowc(ptr str long) ucrtbase.mbtowc
diff --git a/dlls/msvcr100/msvcr100.spec b/dlls/msvcr100/msvcr100.spec
index 6fde8dfe933..efbd6880bf5 100644
--- a/dlls/msvcr100/msvcr100.spec
+++ b/dlls/msvcr100/msvcr100.spec
@@ -1745,7 +1745,7 @@
 @ cdecl mbrlen(ptr long ptr) MSVCRT_mbrlen
 @ cdecl mbrtowc(ptr str long ptr) MSVCRT_mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) MSVCRT_mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) MSVCRT_mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) MSVCRT_mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) MSVCRT__mbstowcs_s
 @ cdecl mbtowc(ptr str long) MSVCRT_mbtowc
diff --git a/dlls/msvcr110/msvcr110.spec b/dlls/msvcr110/msvcr110.spec
index ddab904b809..7476995be4e 100644
--- a/dlls/msvcr110/msvcr110.spec
+++ b/dlls/msvcr110/msvcr110.spec
@@ -2103,7 +2103,7 @@
 @ cdecl mbrlen(ptr long ptr) MSVCRT_mbrlen
 @ cdecl mbrtowc(ptr str long ptr) MSVCRT_mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) MSVCRT_mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) MSVCRT_mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) MSVCRT_mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) MSVCRT__mbstowcs_s
 @ cdecl mbtowc(ptr str long) MSVCRT_mbtowc
diff --git a/dlls/msvcr120/msvcr120.spec b/dlls/msvcr120/msvcr120.spec
index 7efcb209dae..7aa2d191827 100644
--- a/dlls/msvcr120/msvcr120.spec
+++ b/dlls/msvcr120/msvcr120.spec
@@ -2280,7 +2280,7 @@
 @ cdecl mbrlen(ptr long ptr) MSVCRT_mbrlen
 @ cdecl mbrtowc(ptr str long ptr) MSVCRT_mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) MSVCRT_mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) MSVCRT_mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) MSVCRT_mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) MSVCRT__mbstowcs_s
 @ cdecl mbtowc(ptr str long) MSVCRT_mbtowc
diff --git a/dlls/msvcr120_app/msvcr120_app.spec b/dlls/msvcr120_app/msvcr120_app.spec
index 6bfc0b721a2..893c0997838 100644
--- a/dlls/msvcr120_app/msvcr120_app.spec
+++ b/dlls/msvcr120_app/msvcr120_app.spec
@@ -1943,7 +1943,7 @@
 @ cdecl mbrlen(ptr long ptr) msvcr120.mbrlen
 @ cdecl mbrtowc(ptr str long ptr) msvcr120.mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) msvcr120.mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) msvcr120.mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) msvcr120.mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) msvcr120.mbstowcs_s
 @ cdecl mbtowc(ptr str long) msvcr120.mbtowc
diff --git a/dlls/msvcr80/msvcr80.spec b/dlls/msvcr80/msvcr80.spec
index 97f50977d52..a6f0a90f0f7 100644
--- a/dlls/msvcr80/msvcr80.spec
+++ b/dlls/msvcr80/msvcr80.spec
@@ -1425,7 +1425,7 @@
 @ cdecl mbrlen(ptr long ptr) MSVCRT_mbrlen
 @ cdecl mbrtowc(ptr str long ptr) MSVCRT_mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) MSVCRT_mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) MSVCRT_mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) MSVCRT_mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) MSVCRT__mbstowcs_s
 @ cdecl mbtowc(ptr str long) MSVCRT_mbtowc
diff --git a/dlls/msvcr90/msvcr90.spec b/dlls/msvcr90/msvcr90.spec
index 4a29dedd20d..48aed2c3f72 100644
--- a/dlls/msvcr90/msvcr90.spec
+++ b/dlls/msvcr90/msvcr90.spec
@@ -1398,7 +1398,7 @@
 @ cdecl mbrlen(ptr long ptr) MSVCRT_mbrlen
 @ cdecl mbrtowc(ptr str long ptr) MSVCRT_mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) MSVCRT_mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) MSVCRT_mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) MSVCRT_mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) MSVCRT__mbstowcs_s
 @ cdecl mbtowc(ptr str long) MSVCRT_mbtowc
diff --git a/dlls/msvcrt/mbcs.c b/dlls/msvcrt/mbcs.c
index 47478a3d8a3..3e71c91efd9 100644
--- a/dlls/msvcrt/mbcs.c
+++ b/dlls/msvcrt/mbcs.c
@@ -2370,6 +2370,35 @@ MSVCRT_size_t CDECL MSVCRT_mbsrtowcs(MSVCRT_wchar_t *wcstr,
     return ret;
 }
 
+/*********************************************************************
+ *              mbsrtowcs_s(MSVCRT.@)
+ */
+int CDECL MSVCRT_mbsrtowcs_s(MSVCRT_size_t *ret, MSVCRT_wchar_t *wcstr, MSVCRT_size_t len,
+        const char **mbstr, MSVCRT_size_t count, MSVCRT_mbstate_t *state)
+{
+    MSVCRT_size_t tmp;
+
+    if(!ret) ret = &tmp;
+    if(!MSVCRT_CHECK_PMT(!!wcstr == !!len)) {
+        *ret = -1;
+        return MSVCRT_EINVAL;
+    }
+
+    *ret = MSVCRT_mbsrtowcs(wcstr, mbstr, count>len ? len : count, state);
+    if(*ret == -1) {
+        if(wcstr) *wcstr = 0;
+        return *MSVCRT__errno();
+    }
+    (*ret)++;
+    if(*ret > len) {
+        /* no place for terminating '\0' */
+        if(wcstr) *wcstr = 0;
+        return 0;
+    }
+    if(wcstr) wcstr[(*ret)-1] = 0;
+    return 0;
+}
+
 /*********************************************************************
  *		_mbctohira (MSVCRT.@)
  *
diff --git a/dlls/msvcrt/msvcrt.spec b/dlls/msvcrt/msvcrt.spec
index d485a0ed742..37107d58cf7 100644
--- a/dlls/msvcrt/msvcrt.spec
+++ b/dlls/msvcrt/msvcrt.spec
@@ -1365,7 +1365,7 @@
 @ cdecl mbrtowc(ptr str long ptr) MSVCRT_mbrtowc
 # stub mbsdup_dbg(wstr long ptr long)
 @ cdecl mbsrtowcs(ptr ptr long ptr) MSVCRT_mbsrtowcs
-# stub mbsrtowcs_s(ptr ptr long ptr long ptr)
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) MSVCRT_mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) MSVCRT_mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) MSVCRT__mbstowcs_s
 @ cdecl mbtowc(ptr str long) MSVCRT_mbtowc
diff --git a/dlls/ucrtbase/ucrtbase.spec b/dlls/ucrtbase/ucrtbase.spec
index cfb2a0a1ab1..bda6d3df935 100644
--- a/dlls/ucrtbase/ucrtbase.spec
+++ b/dlls/ucrtbase/ucrtbase.spec
@@ -2415,7 +2415,7 @@
 @ stub mbrtoc32
 @ cdecl mbrtowc(ptr str long ptr) MSVCRT_mbrtowc
 @ cdecl mbsrtowcs(ptr ptr long ptr) MSVCRT_mbsrtowcs
-@ stub mbsrtowcs_s
+@ cdecl mbsrtowcs_s(ptr ptr long ptr long ptr) MSVCRT_mbsrtowcs_s
 @ cdecl mbstowcs(ptr str long) MSVCRT_mbstowcs
 @ cdecl mbstowcs_s(ptr ptr long str long) MSVCRT__mbstowcs_s
 @ cdecl mbtowc(ptr str long) MSVCRT_mbtowc