diff --git a/tunnel/tcp.go b/tunnel/tcp.go
index ba4b0b4..7816116 100644
--- a/tunnel/tcp.go
+++ b/tunnel/tcp.go
@@ -72,17 +72,13 @@ func relay(left, right net.Conn) {
 	wg.Wait()
 }
 
-func copyBuffer(dst io.Writer, src io.Reader) (err error) {
+func copyBuffer(dst io.Writer, src io.Reader) error {
 	buf := pool.Get(pool.RelayBufferSize)
 	defer pool.Put(buf)
 
-	defer func() {
-		if err != nil {
-			if ne, ok := err.(net.Error); ok && ne.Timeout() {
-				err = nil /* ignore I/O timeout */
-			}
-		}
-	}()
-	_, err = io.CopyBuffer(dst, src, buf)
+	_, err := io.CopyBuffer(dst, src, buf)
+	if ne, ok := err.(net.Error); ok && ne.Timeout() {
+		return nil /* ignore I/O timeout */
+	}
 	return err
 }
diff --git a/tunnel/udp.go b/tunnel/udp.go
index 80d74f7..c059ba6 100644
--- a/tunnel/udp.go
+++ b/tunnel/udp.go
@@ -86,10 +86,9 @@ func copyPacketBuffer(dst net.PacketConn, src net.PacketConn, to net.Addr, timeo
 	for {
 		src.SetReadDeadline(time.Now().Add(timeout))
 		n, _, err := src.ReadFrom(buf)
-		if err != nil {
-			if ne, ok := err.(net.Error); ok && ne.Timeout() {
-				return nil /* ignore I/O timeout */
-			}
+		if ne, ok := err.(net.Error); ok && ne.Timeout() {
+			return nil /* ignore I/O timeout */
+		} else if err != nil {
 			return err
 		}