diff --git a/tun/tun_netbsd.go b/tun/tun_netbsd.go
index 14fe796..1fb7d5c 100644
--- a/tun/tun_netbsd.go
+++ b/tun/tun_netbsd.go
@@ -37,6 +37,7 @@ type NativeTun struct {
 	events      chan Event
 	errors      chan error
 	routeSocket int
+	closeOnce   sync.Once
 }
 
 func (tun *NativeTun) routineRouteListener(tunIfindex int) {