diff --git a/core/device/fdbased/fd.go b/core/device/fdbased/fd.go
index 20ae348..7528db0 100644
--- a/core/device/fdbased/fd.go
+++ b/core/device/fdbased/fd.go
@@ -1,5 +1,3 @@
 package fdbased
 
 const Driver = "fd"
-
-const defaultMTU = 1500
diff --git a/core/device/fdbased/fd_unix.go b/core/device/fdbased/fd_unix.go
index 269ce1b..678bf1e 100644
--- a/core/device/fdbased/fd_unix.go
+++ b/core/device/fdbased/fd_unix.go
@@ -12,6 +12,8 @@ import (
 	"github.com/xjasonlyu/tun2socks/v2/core/device"
 )
 
+const defaultMTU = 1500
+
 type FD struct {
 	stack.LinkEndpoint