diff --git a/modules/rostests/apitests/crt/_mbsncat.c b/modules/rostests/apitests/crt/_mbsncat.c
new file mode 100644
index 00000000000..392ca1026f0
--- /dev/null
+++ b/modules/rostests/apitests/crt/_mbsncat.c
@@ -0,0 +1,31 @@
+/*
+ * PROJECT:         ReactOS API tests
+ * LICENSE:         LGPL-2.1-or-later (https://spdx.org/licenses/LGPL-2.1-or-later)
+ * PURPOSE:         Tests for _mbsnbcat
+ * COPYRIGHT:       Copyright 2025 Doug Lyons (douglyons@douglyons.com)
+ */
+
+#include <apitest.h>
+#include <mbstring.h>
+#define WIN32_NO_STATUS
+
+START_TEST(_mbsncat)
+{
+    /* use function pointer to bypass gcc builtin */
+    unsigned char *(__cdecl *p__mbsnbcat)(unsigned char*,const unsigned char*,size_t);
+    p__mbsnbcat = (void *)GetProcAddress( GetModuleHandleA("msvcrt.dll"), "_mbsnbcat");
+
+
+    unsigned char dest[16];
+    const unsigned char first[] = "dinosaur";
+    const unsigned char second[] = "duck";
+    unsigned char *s;
+
+    memset(dest, 'X', sizeof(dest));
+    memcpy(dest, first, sizeof(first));
+    s = p__mbsnbcat(dest, second, sizeof(second) - 1);
+    ok(!memcmp(dest, "dinosaurduck", sizeof("dinosaurduck")),
+       "Expected the output buffer string to be \"dinosaurduck\", got '%s'\n", dest);
+    ok(!memcmp(s, "dinosaurduck", sizeof("dinosaurduck")),
+       "Expected the output buffer string to be \"dinosaurduck\", got '%s'\n", dest);
+}
diff --git a/modules/rostests/apitests/crtdll/CMakeLists.txt b/modules/rostests/apitests/crtdll/CMakeLists.txt
index 4a4a012c374..ebb6049786e 100644
--- a/modules/rostests/apitests/crtdll/CMakeLists.txt
+++ b/modules/rostests/apitests/crtdll/CMakeLists.txt
@@ -1,5 +1,6 @@
 
 list(APPEND SOURCE_CRTDLL
+    ../crt/_mbsncat.c
     ../crt/_mbsncmp.c
     ../crt/_mbsstr.c
     ../crt/setjmp.c
diff --git a/modules/rostests/apitests/crtdll/testlist.c b/modules/rostests/apitests/crtdll/testlist.c
index 53eaab58e40..a7681a1a0ab 100644
--- a/modules/rostests/apitests/crtdll/testlist.c
+++ b/modules/rostests/apitests/crtdll/testlist.c
@@ -2,6 +2,7 @@
 #define STANDALONE
 #include <apitest.h>
 
+extern void func__mbsncat(void);
 extern void func__mbsncmp(void);
 extern void func__mbsstr(void);
 extern void func__snprintf(void);
@@ -22,6 +23,7 @@ extern void func_wctomb(void);
 
 const struct test winetest_testlist[] =
 {
+    { "_mbsncat", func__mbsncat },
     { "_mbsncmp", func__mbsncmp },
     { "_mbsstr", func__mbsstr },
     { "_snprintf", func__snprintf },