diff --git a/main.go b/main.go
index 8ae075c..60fe015 100644
--- a/main.go
+++ b/main.go
@@ -36,10 +36,15 @@ var (
 func main() {
 	iphost := flag.String("l", "127.0.0.1:5345", "listen DNS UDP port")
 	fbsrv := flag.String("fb", "127.0.0.1:53", "fallback to DNS UDP port")
+	debug := flag.Bool("d", false, "show debuf log")
 	flag.BoolVar(&forcefb, "ffb", false, "force using fallback")
 	frag := flag.Uint("frag", 3, "TLS first fragemt size")
 	flag.Parse()
 
+	if *debug {
+		logrus.SetLevel(logrus.DebugLevel)
+	}
+
 	if frag != nil {
 		terasu.DefaultFirstFragmentLen = uint8(*frag)
 	}