diff --git a/dlls/ntdll/ntdll_misc.h b/dlls/ntdll/ntdll_misc.h
index 306b36d5bb7..1d56da8525a 100644
--- a/dlls/ntdll/ntdll_misc.h
+++ b/dlls/ntdll/ntdll_misc.h
@@ -156,6 +156,9 @@ extern int ntdll_umbstowcs(DWORD flags, const char* src, int srclen, WCHAR* dst,
 extern int ntdll_wcstoumbs(DWORD flags, const WCHAR* src, int srclen, char* dst, int dstlen,
                            const char* defchar, int *used );
 
+extern int CDECL NTDLL__vsnprintf( char *str, SIZE_T len, const char *format, __ms_va_list args );
+extern int CDECL NTDLL__vsnwprintf( WCHAR *str, SIZE_T len, const WCHAR *format, __ms_va_list args );
+
 /* load order */
 
 enum loadorder
diff --git a/dlls/ntdll/rtl.c b/dlls/ntdll/rtl.c
index f84c7c4fb2c..602bfadbb76 100644
--- a/dlls/ntdll/rtl.c
+++ b/dlls/ntdll/rtl.c
@@ -303,11 +303,11 @@ void WINAPI RtlDumpResource(LPRTL_RWLOCK rwl)
 NTSTATUS WINAPIV DbgPrint(LPCSTR fmt, ...)
 {
   char buf[512];
-  va_list args;
+  __ms_va_list args;
 
-  va_start(args, fmt);
-  vsprintf(buf,fmt, args);
-  va_end(args);
+  __ms_va_start(args, fmt);
+  NTDLL__vsnprintf(buf, sizeof(buf), fmt, args);
+  __ms_va_end(args);
 
   MESSAGE("DbgPrint says: %s",buf);
   /* hmm, raise exception? */
@@ -321,18 +321,18 @@ NTSTATUS WINAPIV DbgPrint(LPCSTR fmt, ...)
 NTSTATUS WINAPIV DbgPrintEx(ULONG iComponentId, ULONG Level, LPCSTR fmt, ...)
 {
     NTSTATUS ret;
-    va_list args;
+    __ms_va_list args;
 
-    va_start(args, fmt);
+    __ms_va_start(args, fmt);
     ret = vDbgPrintEx(iComponentId, Level, fmt, args);
-    va_end(args);
+    __ms_va_end(args);
     return ret;
 }
 
 /******************************************************************************
  *	vDbgPrintEx	[NTDLL.@]
  */
-NTSTATUS WINAPI vDbgPrintEx( ULONG id, ULONG level, LPCSTR fmt, va_list args )
+NTSTATUS WINAPI vDbgPrintEx( ULONG id, ULONG level, LPCSTR fmt, __ms_va_list args )
 {
     return vDbgPrintExWithPrefix( "", id, level, fmt, args );
 }
@@ -340,11 +340,11 @@ NTSTATUS WINAPI vDbgPrintEx( ULONG id, ULONG level, LPCSTR fmt, va_list args )
 /******************************************************************************
  *	vDbgPrintExWithPrefix  [NTDLL.@]
  */
-NTSTATUS WINAPI vDbgPrintExWithPrefix( LPCSTR prefix, ULONG id, ULONG level, LPCSTR fmt, va_list args )
+NTSTATUS WINAPI vDbgPrintExWithPrefix( LPCSTR prefix, ULONG id, ULONG level, LPCSTR fmt, __ms_va_list args )
 {
     char buf[1024];
 
-    vsprintf(buf, fmt, args);
+    NTDLL__vsnprintf(buf, sizeof(buf), fmt, args);
 
     switch (level & DPFLTR_MASK)
     {
diff --git a/include/winternl.h b/include/winternl.h
index 1a11469bccc..1af1370aed2 100644
--- a/include/winternl.h
+++ b/include/winternl.h
@@ -2508,8 +2508,8 @@ NTSYSAPI NTSTATUS  WINAPI RtlpNtCreateKey(PHANDLE,ACCESS_MASK,const OBJECT_ATTRI
 NTSYSAPI NTSTATUS  WINAPI RtlpNtEnumerateSubKey(HANDLE,UNICODE_STRING *, ULONG);
 NTSYSAPI NTSTATUS  WINAPI RtlpWaitForCriticalSection(RTL_CRITICAL_SECTION *);
 NTSYSAPI NTSTATUS  WINAPI RtlpUnWaitCriticalSection(RTL_CRITICAL_SECTION *);
-NTSYSAPI NTSTATUS  WINAPI vDbgPrintEx(ULONG,ULONG,LPCSTR,va_list);
-NTSYSAPI NTSTATUS  WINAPI vDbgPrintExWithPrefix(LPCSTR,ULONG,ULONG,LPCSTR,va_list);
+NTSYSAPI NTSTATUS  WINAPI vDbgPrintEx(ULONG,ULONG,LPCSTR,__ms_va_list);
+NTSYSAPI NTSTATUS  WINAPI vDbgPrintExWithPrefix(LPCSTR,ULONG,ULONG,LPCSTR,__ms_va_list);
 
 /* Wine internal functions */