diff --git a/monitor_shared.go b/monitor_shared.go
index 12e3e21..265b07d 100644
--- a/monitor_shared.go
+++ b/monitor_shared.go
@@ -66,7 +66,12 @@ func (m *defaultInterfaceMonitor) Start() error {
 	return nil
 }
 
+var accessDelayCheckUpdate sync.Mutex
+
 func (m *defaultInterfaceMonitor) delayCheckUpdate() {
+	accessDelayCheckUpdate.Lock()
+	defer accessDelayCheckUpdate.Unlock()
+
 	if m.checkUpdateTimer == nil {
 		m.checkUpdateTimer = time.AfterFunc(time.Second, m.postCheckUpdate)
 	} else {
diff --git a/stack_system_nat.go b/stack_system_nat.go
index 1d0216e..8dc412a 100644
--- a/stack_system_nat.go
+++ b/stack_system_nat.go
@@ -66,7 +66,9 @@ func (n *TCPNat) LookupBack(port uint16) *TCPSession {
 	session := n.portMap[port]
 	n.portAccess.RUnlock()
 	if session != nil {
+		n.portAccess.Lock()
 		session.LastActive = time.Now()
+		n.portAccess.Unlock()
 	}
 	return session
 }