From b11532744d60212673e84467bead30ef6a0a16ed Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Thu, 22 Jan 2026 14:08:12 +0200
Subject: [PATCH] [MSVCRT] Fix _mbsnbcat_l parameter check

---
 dll/win32/msvcrt/mbcs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/dll/win32/msvcrt/mbcs.c b/dll/win32/msvcrt/mbcs.c
index bd4245c2c53..2637d13ae88 100644
--- a/dll/win32/msvcrt/mbcs.c
+++ b/dll/win32/msvcrt/mbcs.c
@@ -2513,6 +2513,11 @@ unsigned char* CDECL _mbsnbcat_l(unsigned char *dst, const unsigned char *src, s
 {
     pthreadmbcinfo mbcinfo;
 
+#ifdef __REACTOS__
+    if (!len)
+        return dst;
+#endif
+
     if (!MSVCRT_CHECK_PMT(dst && src))
         return NULL;