diff --git a/client.go b/client.go
index 56890ef..7eb996a 100644
--- a/client.go
+++ b/client.go
@@ -406,7 +406,7 @@ func (c *TunaSessionClient) listenNet(i int) {
 	for {
 		netConn, err := c.listeners[i].Accept()
 		if err != nil {
-			if c.IsClosed() {
+			if c.isClosed {
 				return
 			}
 			log.Printf("Accept connection error: %v", err)
@@ -877,7 +877,7 @@ func (c *TunaSessionClient) removeClosedSessions() {
 	for {
 		time.Sleep(time.Second)
 
-		if c.IsClosed() {
+		if c.isClosed {
 			return
 		}
 
@@ -1011,7 +1011,7 @@ func (c *TunaSessionClient) dialTcpConn(ctx context.Context, remoteAddr string,
 }
 
 func (c *TunaSessionClient) reconnect(remoteAddr string, sessionID []byte, i int, pubAddrs *PubAddrs, config *nkn.DialConfig) (conn *Conn, err error) {
-	if c.IsClosed() {
+	if c.isClosed {
 		return nil, ErrClosed
 	}
 	sessKey := sessionKey(remoteAddr, sessionID)
diff --git a/udp.go b/udp.go
index 1787c02..324bd3d 100644
--- a/udp.go
+++ b/udp.go
@@ -81,7 +81,7 @@ func (c *TunaSessionClient) DialUDPWithConfig(remoteAddr string, config *nkn.Dia
 		for {
 			udpSess.handleTcpMsg(udpSess.tcpConn, sessionKey(remoteAddr, sessionID))
 
-			if c.IsClosed() || udpSess.udpConn.IsClosed() {
+			if c.isClosed || udpSess.udpConn.IsClosed() {
 				break
 			}
 			if c.config.ReconnectRetries == 0 {
diff --git a/udpsession.go b/udpsession.go
index 8616ec6..396c683 100644
--- a/udpsession.go
+++ b/udpsession.go
@@ -79,7 +79,7 @@ func newUdpSession(ts *TunaSessionClient, isListener bool) *UdpSession {
 }
 
 func (us *UdpSession) DialUpSession(listenerNknAddr string, sessionID []byte, config *nkn.DialConfig) (err error) {
-	if us.ts.IsClosed() {
+	if us.ts.isClosed {
 		return ErrClosed
 	}
 
@@ -203,7 +203,7 @@ func (us *UdpSession) GetUDPConn() *tuna.EncryptUDPConn {
 }
 
 func (us *UdpSession) GetEstablishedUDPConn() (*tuna.EncryptUDPConn, error) {
-	if us.ts.IsClosed() {
+	if us.ts.isClosed {
 		return nil, ErrClosed
 	}
 	conn := us.GetUDPConn()
@@ -315,7 +315,7 @@ func (us *UdpSession) Write(b []byte) (int, error) {
 }
 
 func (us *UdpSession) SetDeadline(t time.Time) error {
-	if us.ts.IsClosed() {
+	if us.ts.isClosed {
 		return ErrClosed
 	}