diff --git a/pulsar/ack_grouping_tracker.go b/pulsar/ack_grouping_tracker.go
index dd051868d7..97d9e05a64 100644
--- a/pulsar/ack_grouping_tracker.go
+++ b/pulsar/ack_grouping_tracker.go
@@ -120,7 +120,7 @@ type timedAckGroupingTracker struct {
 
 	// Key is the pair of the ledger id and the entry id,
 	// Value is the bit set that represents which messages are acknowledged if the entry stores a batch.
-	// The bit 1 represents the message has been acknowledged, i.e. the bits "111" represents all messages
+	// The bit 1 represents the message has not been acknowledged, i.e. the bits "111" represents all messages
 	// in the batch whose batch size is 3 are not acknowledged.
 	// After the 1st message (i.e. batch index is 0) is acknowledged, the bits will become "011".
 	// Value is nil if the entry represents a single message.
@@ -241,6 +241,9 @@ func (t *timedAckGroupingTracker) clearPendingAcks() map[[2]uint64]*bitset.BitSe
 }
 
 func (t *timedAckGroupingTracker) close() {
+	if t.ticker != nil {
+		t.ticker.Stop()
+	}
 	t.flushAndClean()
 	if t.exitCh != nil {
 		close(t.exitCh)
diff --git a/pulsar/ack_grouping_tracker_test.go b/pulsar/ack_grouping_tracker_test.go
index 0a794f6403..202d19d9d5 100644
--- a/pulsar/ack_grouping_tracker_test.go
+++ b/pulsar/ack_grouping_tracker_test.go
@@ -217,6 +217,52 @@ func TestDuplicateAfterClose(t *testing.T) {
 	assert.False(t, tracker.isDuplicate(&messageID{ledgerID: 1}))
 }
 
+func TestCloseFlushWithoutTimer(t *testing.T) {
+	var acker mockAcker
+	tracker := newAckGroupingTracker(
+		&AckGroupingOptions{MaxSize: 3, MaxTime: 0},
+		nil,
+		func(id MessageID) { acker.ackCumulative(id) },
+		func(ids []*pb.MessageIdData) { acker.ack(ids) },
+	)
+
+	// case 1: message will not be acked because the cache is not full
+	tracker.add(&messageID{ledgerID: 1})
+	tracker.add(&messageID{ledgerID: 2})
+	assert.True(t, tracker.isDuplicate(&messageID{ledgerID: int64(1)}))
+	assert.True(t, tracker.isDuplicate(&messageID{ledgerID: int64(2)}))
+	assert.Equal(t, 0, len(acker.getLedgerIDs()))
+
+	// case 2: tracker close so that all messages are flushed and acked
+	tracker.close()
+	assert.False(t, tracker.isDuplicate(&messageID{ledgerID: 1}))
+	assert.False(t, tracker.isDuplicate(&messageID{ledgerID: 2}))
+	assert.Equal(t, []int64{1, 2}, acker.getLedgerIDs())
+}
+
+func TestCloseFlushWithTimer(t *testing.T) {
+	var acker mockAcker
+	tracker := newAckGroupingTracker(
+		&AckGroupingOptions{MaxSize: 1000, MaxTime: 10 * 1000},
+		nil,
+		func(id MessageID) { acker.ackCumulative(id) },
+		func(ids []*pb.MessageIdData) { acker.ack(ids) },
+	)
+
+	// case 1: messages are not acked because the cache is not full
+	tracker.add(&messageID{ledgerID: 1})
+	tracker.add(&messageID{ledgerID: 2})
+	assert.True(t, tracker.isDuplicate(&messageID{ledgerID: int64(1)}))
+	assert.True(t, tracker.isDuplicate(&messageID{ledgerID: int64(2)}))
+	assert.Equal(t, 0, len(acker.getLedgerIDs()))
+
+	// case 2: tracker close so that all messages are flushed and acked
+	tracker.close()
+	assert.False(t, tracker.isDuplicate(&messageID{ledgerID: 1}))
+	assert.False(t, tracker.isDuplicate(&messageID{ledgerID: 2}))
+	assert.Equal(t, []int64{1, 2}, acker.getLedgerIDs())
+}
+
 func TestTrackerPendingAcks(t *testing.T) {
 	m := make(map[uint64][]int64)
 	tracker := newAckGroupingTracker(&AckGroupingOptions{MaxSize: 3, MaxTime: 0}, nil, nil,