diff --git a/client/client.go b/client/client.go
index 8ecf8112..361a7530 100644
--- a/client/client.go
+++ b/client/client.go
@@ -77,6 +77,8 @@ type QQClient struct {
 
 	groupListLock sync.Mutex
 	msgSvcLock    sync.Mutex
+
+	seqLock sync.Mutex
 }
 
 type loginSigInfo struct {
@@ -818,6 +820,9 @@ func (c *QQClient) registerClient() {
 }
 
 func (c *QQClient) nextSeq() uint16 {
+	c.seqLock.Lock()
+	defer c.seqLock.Unlock()
+
 	c.SequenceId++
 	c.SequenceId &= 0x7FFF
 	if c.SequenceId == 0 {