diff --git a/nagios/cgi/cmd.c b/nagios/cgi/cmd.c

index c9a6996..0941a75 100644

--- a/nagios/cgi/cmd.c

+++ b/nagios/cgi/cmd.c

@@ -1902,14 +1902,16 @@ static int cmd_submitf(int id, const char *fmt, ...)

 		return ERROR;

 	len = snprintf(cmd, sizeof(cmd) - 1, "[%lu] %s;", time(NULL), command);

-	if (len < 0)

+	if (len < 0 || len >= sizeof(cmd))

 		return ERROR;

-	va_start(ap, fmt);

-	len2 = vsnprintf(&cmd[len], sizeof(cmd) - len - 1, fmt, ap);

-	va_end(ap);

-	if (len2 < 0)

-		return ERROR;

+    if (fmt) {

+        va_start(ap, fmt);

+        len2 = vsnprintf(&cmd[len], sizeof(cmd) - len - 1, fmt, ap);

+        va_end(ap);

+        if (len2 < 0 || len2 >= sizeof(cmd))

+            return ERROR;

+    }

 	return write_command_to_file(cmd);

 }