diff --git a/delayqueue.go b/delayqueue.go
index fc86238..5ab9e4d 100644
--- a/delayqueue.go
+++ b/delayqueue.go
@@ -200,7 +200,7 @@ func (q *DelayQueue) pending2Ready() error {
 	return nil
 }
 
-// pending2ReadyScript atomically moves messages from ready to unack
+// ready2UnackScript atomically moves messages from ready to unack
 // keys: readyKey/retryKey, unackKey
 // argv: retryTime
 const ready2UnackScript = `
@@ -338,7 +338,7 @@ local unack2retry = function(msgs)
 	local retryCounts = redis.call('HMGet', KEYS[2], unpack(msgs)) -- get retry count
 	for i,v in ipairs(retryCounts) do
 		local k = msgs[i]
-		if tonumber(v) > 0 then
+		if v ~= nil and v ~= '' and tonumber(v) > 0 then
 			redis.call("HIncrBy", KEYS[2], k, -1) -- reduce retry count
 			redis.call("LPush", KEYS[3], k) -- add to retry
 		else
diff --git a/delayqueue_test.go b/delayqueue_test.go
index 4036a23..9d86f08 100644
--- a/delayqueue_test.go
+++ b/delayqueue_test.go
@@ -16,7 +16,7 @@ func TestDelayQueue_consume(t *testing.T) {
 		Addr: "127.0.0.1:6379",
 	})
 	redisCli.FlushDB(context.Background())
-	size := 10000
+	size := 1000
 	retryCount := 3
 	deliveryCount := make(map[string]int)
 	cb := func(s string) bool {
@@ -31,7 +31,7 @@ func TestDelayQueue_consume(t *testing.T) {
 		WithFetchLimit(2)
 
 	for i := 0; i < size; i++ {
-		err := queue.SendDelayMsg(strconv.Itoa(i), 0, WithRetryCount(retryCount),WithMsgTTL(time.Hour))
+		err := queue.SendDelayMsg(strconv.Itoa(i), 0, WithRetryCount(retryCount), WithMsgTTL(time.Hour))
 		if err != nil {
 			t.Error(err)
 		}
@@ -79,7 +79,7 @@ func TestDelayQueue_ConcurrentConsume(t *testing.T) {
 		WithConcurrent(4)
 
 	for i := 0; i < size; i++ {
-		err := queue.SendDelayMsg(strconv.Itoa(i), 0, WithRetryCount(retryCount),WithMsgTTL(time.Hour))
+		err := queue.SendDelayMsg(strconv.Itoa(i), 0, WithRetryCount(retryCount), WithMsgTTL(time.Hour))
 		if err != nil {
 			t.Error(err)
 		}
@@ -123,3 +123,71 @@ func TestDelayQueue_StopConsume(t *testing.T) {
 	done := queue.StartConsume()
 	<-done
 }
+
+func TestDelayQueue_Massive_Consume(t *testing.T) {
+	redisCli := redis.NewClient(&redis.Options{
+		Addr: "127.0.0.1:6379",
+	})
+	redisCli.FlushDB(context.Background())
+	size := 20000
+	retryCount := 3
+	cb := func(s string) bool {
+		return false
+	}
+	q := NewQueue("test", redisCli, cb).
+		WithFetchInterval(time.Millisecond * 50).
+		WithMaxConsumeDuration(0).
+		WithLogger(log.New(os.Stderr, "[DelayQueue]", log.LstdFlags)).
+		WithFetchLimit(0)
+
+	for i := 0; i < size; i++ {
+		err := q.SendDelayMsg(strconv.Itoa(i), 0, WithRetryCount(retryCount))
+		if err != nil {
+			t.Error(err)
+		}
+	}
+	err := q.pending2Ready()
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	// consume
+	ids := make([]string, 0, q.fetchLimit)
+	for {
+		idStr, err := q.ready2Unack()
+		if err == redis.Nil { // consumed all
+			break
+		}
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		ids = append(ids, idStr)
+		if q.fetchLimit > 0 && len(ids) >= int(q.fetchLimit) {
+			break
+		}
+	}
+	err = q.unack2Retry()
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	unackCard, err := redisCli.ZCard(context.Background(), q.unAckKey).Result()
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if unackCard != 0 {
+		t.Error("unack card should be 0")
+		return
+	}
+	retryLen, err := redisCli.LLen(context.Background(), q.retryKey).Result()
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if int(retryLen) != size {
+		t.Errorf("unack card should be %d", size)
+		return
+	}
+}