diff --git a/README.md b/README.md
index 664bff0..d2ad754 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,7 @@ wg [-c config.yaml] [-d|w] [-g] [-h] [-m mtu] [-p]
   -p    show my publickey
   -w    only show logs above warn level
 ```
+- *especially*: in macos mojave, max value of mtu is `9159`
 
 ## Config file example
 ```yaml
diff --git a/lower/tun_darwin.go b/lower/tun_darwin.go
index 745d551..0b0712a 100644
--- a/lower/tun_darwin.go
+++ b/lower/tun_darwin.go
@@ -4,7 +4,7 @@
 package lower
 
 func (n *NIC) Up() {
-	execute("ifconfig", n.ifce.Name(), "mtu", n.mtu)
+	execute("ifconfig", n.ifce.Name(), "mtu", n.mtu) // max: 9159
 	execute("ifconfig", n.ifce.Name(), "inet", n.ip, n.ip, "up")
 	execute("route", "add", n.subnet, "-interface", n.ifce.Name())
 	for _, c := range n.cidrs {