diff --git a/server/consumer.go b/server/consumer.go
index e0b1e04c4b0..56dca38b21a 100644
--- a/server/consumer.go
+++ b/server/consumer.go
@@ -1273,6 +1273,9 @@ func (acc *Account) checkNewConsumerConfig(cfg, ncfg *ConsumerConfig) error {
 		if cfg.DeliverSubject == _EMPTY_ {
 			return errors.New("can not update pull consumer to push based")
 		}
+		if ncfg.DeliverSubject == _EMPTY_ {
+			return errors.New("can not update push consumer to pull based")
+		}
 		rr := acc.sl.Match(cfg.DeliverSubject)
 		if len(rr.psubs)+len(rr.qsubs) != 0 {
 			return NewJSConsumerNameExistError()
@@ -2330,7 +2333,7 @@ func (o *consumer) processNextMsgReq(_ *subscription, c *client, _ *Account, _,
 		o.outq.send(newJSPubMsg(reply, _EMPTY_, _EMPTY_, hdr, nil, nil, 0))
 	}
 
-	if o.isPushMode() {
+	if o.isPushMode() || o.waiting == nil {
 		sendErr(409, "Consumer is push based")
 		return
 	}
diff --git a/server/jetstream_cluster_test.go b/server/jetstream_cluster_test.go
index fe44c833ba1..ba08c9bcbfb 100644
--- a/server/jetstream_cluster_test.go
+++ b/server/jetstream_cluster_test.go
@@ -10360,6 +10360,36 @@ func TestJetStreamClusterRedeliverBackoffs(t *testing.T) {
 	}
 }
 
+func TestJetStreamConsumerUpgrade(t *testing.T) {
+	s := RunBasicJetStreamServer()
+	defer s.Shutdown()
+
+	if config := s.JetStreamConfig(); config != nil {
+		defer removeDir(t, config.StoreDir)
+	}
+
+	c := createJetStreamClusterExplicit(t, "JSC", 3)
+	defer c.shutdown()
+
+	testUpdate := func(t *testing.T, s *Server) {
+		nc, js := jsClientConnect(t, s)
+		defer nc.Close()
+		_, err := js.AddStream(&nats.StreamConfig{Name: "X"})
+		require_NoError(t, err)
+		_, err = js.Publish("X", []byte("OK"))
+		require_NoError(t, err)
+		// First create a consumer that is push based.
+		_, err = js.AddConsumer("X", &nats.ConsumerConfig{Durable: "dlc", DeliverSubject: "Y"})
+		require_NoError(t, err)
+		// Now do same name but pull. This should be an error.
+		_, err = js.AddConsumer("X", &nats.ConsumerConfig{Durable: "dlc"})
+		require_Error(t, err)
+	}
+
+	t.Run("Single", func(t *testing.T) { testUpdate(t, s) })
+	t.Run("Clustered", func(t *testing.T) { testUpdate(t, c.randomServer()) })
+}
+
 // Support functions
 
 // Used to setup superclusters for tests.