diff --git a/core.go b/core.go
index f703fc591..003040dd9 100755
--- a/core.go
+++ b/core.go
@@ -17,7 +17,7 @@ import (
 )
 
 const (
-	version  = "4.21.0"
+	version  = "4.21.1"
 	build    = "Custom"
 	codename = "V2Fly, a community-driven edition of V2Ray."
 	intro    = "A unified platform for anti-censorship."
diff --git a/go.mod b/go.mod
index 888cd2ba1..9bb0da48f 100644
--- a/go.mod
+++ b/go.mod
@@ -11,6 +11,7 @@ require (
 	golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2
 	golang.org/x/net v0.0.0-20190311183353-d8887717615a
 	golang.org/x/sync v0.0.0-20190423024810-112230192c58
+	golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a
 	google.golang.org/genproto v0.0.0-20180831171423-11092d34479b // indirect
 	google.golang.org/grpc v1.24.0
 	h12.io/socks v1.0.0