diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
index c0318adf56a13..ea668826e089b 100644
--- a/sessionctx/variable/session.go
+++ b/sessionctx/variable/session.go
@@ -3181,8 +3181,9 @@ func (s *SessionVars) GetNegateStrMatchDefaultSelectivity() float64 {
 
 // GetRelatedTableForMDL gets the related table for metadata lock.
 func (s *SessionVars) GetRelatedTableForMDL() *sync.Map {
-	s.TxnCtx.tdmLock.Lock()
-	defer s.TxnCtx.tdmLock.Unlock()
+	mu := &s.TxnCtx.tdmLock
+	mu.Lock()
+	defer mu.Unlock()
 	if s.TxnCtx.relatedTableForMDL == nil {
 		s.TxnCtx.relatedTableForMDL = new(sync.Map)
 	}