diff --git a/src/yggdrasil/tun_darwin.go b/src/yggdrasil/tun_darwin.go
index 4793a5c..efd9845 100644
--- a/src/yggdrasil/tun_darwin.go
+++ b/src/yggdrasil/tun_darwin.go
@@ -2,12 +2,11 @@ package yggdrasil
 
 // The darwin platform specific tun parts
 
-import "syscall"
 import "unsafe"
 import "strings"
 import "strconv"
 import "encoding/binary"
-// import "fmt"
+import "golang.org/x/sys/unix"
 
 import water "github.com/songgao/water"
 
@@ -22,8 +21,6 @@ func (tun *tunDevice) setup(ifname string, addr string, mtu int) error {
 	return tun.setupAddress(addr)
 }
 
-const AF_INET6 = 30
-const IN6_IFF_NODAD = 0x0020
 const SIOCAIFADDR_IN6 = 2155899162
 
 type in6_addrlifetime struct {
@@ -51,11 +48,16 @@ type in6_aliasreq struct {
 	ifra_lifetime   in6_addrlifetime
 }
 
+type ifreq struct {
+	ifr_name				[16]byte
+	ifru_mtu				uint32
+}
+
 func (tun *tunDevice) setupAddress(addr string) error {
 	var fd int
 	var err error
 
-	if fd, err = syscall.Socket(syscall.AF_INET6, syscall.SOCK_DGRAM, 0); err != nil {
+	if fd, err = unix.Socket(unix.AF_INET6, unix.SOCK_DGRAM, 0); err != nil {
 		tun.core.log.Printf("Create AF_SYSTEM socket failed: %v.", err)
 		return err
 	}
@@ -68,7 +70,7 @@ func (tun *tunDevice) setupAddress(addr string) error {
 	ar.ifra_prefixmask.sin6_addr[0] = uint16(binary.BigEndian.Uint16(b))
 
 	ar.ifra_addr.sin6_len = uint8(unsafe.Sizeof(ar.ifra_addr))
-	ar.ifra_addr.sin6_family = AF_INET6
+	ar.ifra_addr.sin6_family = unix.AF_INET6
 	parts := strings.Split(strings.TrimRight(addr, "/8"), ":")
 	for i := 0; i < 8; i++ {
 		addr, _ := strconv.ParseUint(parts[i], 16, 16)
@@ -79,28 +81,25 @@ func (tun *tunDevice) setupAddress(addr string) error {
 	ar.ifra_lifetime.ia6t_vltime = 0xFFFFFFFF
 	ar.ifra_lifetime.ia6t_pltime = 0xFFFFFFFF
 
+	var ir ifreq
+	copy(ir.ifr_name[:], tun.iface.Name())
+	ir.ifru_mtu = 1280
+
 	tun.core.log.Printf("Interface name: %s", ar.ifra_name)
 	tun.core.log.Printf("Interface IPv6: %s", addr)
+	tun.core.log.Printf("Interface MTU: %d", ir.ifru_mtu)
 
-  /*
-		var bytes *[unsafe.Sizeof(ar)]byte = (*[unsafe.Sizeof(ar)]byte)(unsafe.Pointer(&ar));
-		var out string;
-		for i := 0; i < int(unsafe.Sizeof(ar)); i ++ {
-			out += fmt.Sprintf("0x%02x", (*bytes)[i]);
-			if i % 8 == 7 {
-				out += "\n"
-			} else {
-				out += " "
-			}
-		}
-		tun.core.log.Printf("in6_aliasreq:\n%s", out);
-  */
-
-	if _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), uintptr(SIOCAIFADDR_IN6), uintptr(unsafe.Pointer(&ar))); errno != 0 {
+	if _, _, errno := unix.Syscall(unix.SYS_IOCTL, uintptr(fd), uintptr(SIOCAIFADDR_IN6), uintptr(unsafe.Pointer(&ar))); errno != 0 {
 		err = errno
 		tun.core.log.Printf("Error in SIOCAIFADDR_IN6: %v", errno)
 		return err
 	}
 
+	if _, _, errno := unix.Syscall(unix.SYS_IOCTL, uintptr(fd), uintptr(unix.SIOCSIFMTU), uintptr(unsafe.Pointer(&ir))); errno != 0 {
+		err = errno
+		tun.core.log.Printf("Error in SIOCSIFMTU: %v", errno)
+		return err
+	}
+
 	return err
 }