diff --git a/control.go b/control.go
index 238bc131..63a387b0 100644
--- a/control.go
+++ b/control.go
@@ -218,6 +218,7 @@ func checkDNS(input string) error {
 	if err != nil {
 		return err
 	}
+	defer u.Close()
 
 	alive, err := upstream.IsAlive(u)