diff --git a/pkg/source/pulsar.go b/pkg/source/pulsar.go
index fd332c0..7024b87 100644
--- a/pkg/source/pulsar.go
+++ b/pkg/source/pulsar.go
@@ -307,9 +307,13 @@ func (a *ackTrackers) key(msg pulsar.MessageID) string {
 	return fmt.Sprintf("%d:%d", msg.LedgerID(), msg.EntryID())
 }
 
-func (a *ackTrackers) tryAdd(msg pulsar.MessageID) bool {
-	_, loaded := a.trackers.LoadOrStore(a.key(msg), newAckTracker(uint(msg.BatchSize())))
-	return !loaded
+func (a *ackTrackers) tryAdd(msg pulsar.MessageID) (ok bool) {
+	key := a.key(msg)
+	_, ok = a.trackers.Load(key)
+	if !ok {
+		_, ok = a.trackers.LoadOrStore(key, newAckTracker(uint(msg.BatchSize())))
+	}
+	return !ok
 }
 
 func (a *ackTrackers) tryAck(msg pulsar.MessageID) (success bool, exist bool) {