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);
 }