diff --git a/chain/sub/incoming.go b/chain/sub/incoming.go
index fc2b7baff..3a11f7c98 100644
--- a/chain/sub/incoming.go
+++ b/chain/sub/incoming.go
@@ -529,9 +529,8 @@ func (v *IndexerMessageValidator) Validate(ctx context.Context, pid peer.ID, msg
 
 	msgCid := idxrMsg.Cid
 
-	var msgInfo *peerMsgInfo
-	msgInfo, ok := v.peerCache.Get(minerAddr)
-	if !ok {
+	msgInfo, cached := v.peerCache.Get(minerAddr)
+	if !cached {
 		msgInfo = &peerMsgInfo{}
 	}
 
@@ -539,17 +538,17 @@ func (v *IndexerMessageValidator) Validate(ctx context.Context, pid peer.ID, msg
 	msgInfo.mutex.Lock()
 	defer msgInfo.mutex.Unlock()
 
-	if ok {
+	var seqno uint64
+	if cached {
 		// Reject replayed messages.
-		seqno := binary.BigEndian.Uint64(msg.Message.GetSeqno())
+		seqno = binary.BigEndian.Uint64(msg.Message.GetSeqno())
 		if seqno <= msgInfo.lastSeqno {
 			log.Debugf("ignoring replayed indexer message")
 			return pubsub.ValidationIgnore
 		}
-		msgInfo.lastSeqno = seqno
 	}
 
-	if !ok || originPeer != msgInfo.peerID {
+	if !cached || originPeer != msgInfo.peerID {
 		// Check that the miner ID maps to the peer that sent the message.
 		err = v.authenticateMessage(ctx, minerAddr, originPeer)
 		if err != nil {
@@ -558,7 +557,7 @@ func (v *IndexerMessageValidator) Validate(ctx context.Context, pid peer.ID, msg
 			return pubsub.ValidationReject
 		}
 		msgInfo.peerID = originPeer
-		if !ok {
+		if !cached {
 			// Add msgInfo to cache only after being authenticated.  If two
 			// messages from the same peer are handled concurrently, there is a
 			// small chance that one msgInfo could replace the other here when
@@ -567,6 +566,9 @@ func (v *IndexerMessageValidator) Validate(ctx context.Context, pid peer.ID, msg
 		}
 	}
 
+	// Update message info cache with the latest message's sequence number.
+	msgInfo.lastSeqno = seqno
+
 	// See if message needs to be ignored due to rate limiting.
 	if v.rateLimitPeer(msgInfo, msgCid) {
 		return pubsub.ValidationIgnore
diff --git a/chain/sub/incoming_test.go b/chain/sub/incoming_test.go
index f54e09049..d8ee99b7f 100644
--- a/chain/sub/incoming_test.go
+++ b/chain/sub/incoming_test.go
@@ -12,10 +12,12 @@ import (
 	"github.com/ipni/go-libipni/announce/message"
 	pubsub "github.com/libp2p/go-libp2p-pubsub"
 	pb "github.com/libp2p/go-libp2p-pubsub/pb"
+	"github.com/libp2p/go-libp2p/core/crypto"
 	"github.com/libp2p/go-libp2p/core/peer"
 
 	"github.com/filecoin-project/go-address"
 
+	"github.com/filecoin-project/lotus/api"
 	"github.com/filecoin-project/lotus/api/mocks"
 	"github.com/filecoin-project/lotus/chain/types"
 )
@@ -134,3 +136,123 @@ func TestIndexerMessageValidator_Validate(t *testing.T) {
 		})
 	}
 }
+
+func TestIdxValidator(t *testing.T) {
+	validCid, err := cid.Decode("QmbpDgg5kRLDgMxS8vPKNFXEcA6D5MC4CkuUdSWDVtHPGK")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	addr, err := address.NewFromString("f01024")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	buf1, err := addr.MarshalBinary()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	selfPID := "12D3KooWQiCbqEStCkdqUvr69gQsrp9urYJZUCkzsQXia7mbqbFW"
+	senderPID := "12D3KooWE8yt84RVwW3sFcd6WMjbUdWrZer2YtT4dmtj3dHdahSZ"
+	extraData := buf1
+
+	mc := gomock.NewController(t)
+	node := mocks.NewMockFullNode(mc)
+	node.EXPECT().ChainHead(gomock.Any()).Return(nil, nil).AnyTimes()
+
+	subject := NewIndexerMessageValidator(peer.ID(selfPID), node, node)
+	message := message.Message{
+		Cid:       validCid,
+		Addrs:     nil,
+		ExtraData: extraData,
+	}
+	buf := bytes.NewBuffer(nil)
+	if err := message.MarshalCBOR(buf); err != nil {
+		t.Fatal(err)
+	}
+
+	topic := "topic"
+
+	privk, _, err := crypto.GenerateKeyPair(crypto.RSA, 2048)
+	if err != nil {
+		t.Fatal(err)
+	}
+	id, err := peer.IDFromPublicKey(privk.GetPublic())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	node.EXPECT().StateMinerInfo(gomock.Any(), gomock.Any(), gomock.Any()).Return(api.MinerInfo{PeerId: &id}, nil).AnyTimes()
+
+	pbm := &pb.Message{
+		Data:  buf.Bytes(),
+		Topic: &topic,
+		From:  []byte(id),
+		Seqno: []byte{1, 1, 1, 1, 2, 2, 2, 2},
+	}
+	validate := subject.Validate(context.Background(), peer.ID(senderPID), &pubsub.Message{
+		Message:       pbm,
+		ReceivedFrom:  peer.ID("f01024"), // peer.ID(senderPID),
+		ValidatorData: nil,
+	})
+	if validate != pubsub.ValidationAccept {
+		t.Error("Expected to receive ValidationAccept")
+	}
+	msgInfo, cached := subject.peerCache.Get(addr)
+	if !cached {
+		t.Fatal("Message info should be in cache")
+	}
+	seqno := msgInfo.lastSeqno
+	msgInfo.rateLimit = nil // prevent interference from rate limiting
+
+	t.Log("Sending DoS msg")
+	privk, _, err = crypto.GenerateKeyPair(crypto.RSA, 2048)
+	if err != nil {
+		t.Fatal(err)
+	}
+	id2, err := peer.IDFromPublicKey(privk.GetPublic())
+	if err != nil {
+		t.Fatal(err)
+	}
+	pbm = &pb.Message{
+		Data:  buf.Bytes(),
+		Topic: &topic,
+		From:  []byte(id2),
+		Seqno: []byte{255, 255, 255, 255, 255, 255, 255, 255},
+	}
+	validate = subject.Validate(context.Background(), peer.ID(senderPID), &pubsub.Message{
+		Message:       pbm,
+		ReceivedFrom:  peer.ID(senderPID),
+		ValidatorData: nil,
+	})
+	if validate != pubsub.ValidationReject {
+		t.Error("Expected to get ValidationReject")
+	}
+	msgInfo, cached = subject.peerCache.Get(addr)
+	if !cached {
+		t.Fatal("Message info should be in cache")
+	}
+	msgInfo.rateLimit = nil // prevent interference from rate limiting
+
+	// Check if DoS is possible.
+	if msgInfo.lastSeqno != seqno {
+		t.Fatal("Sequence number should not have been updated")
+	}
+
+	t.Log("Sending another valid message from miner...")
+	pbm = &pb.Message{
+		Data:  buf.Bytes(),
+		Topic: &topic,
+		From:  []byte(id),
+		Seqno: []byte{1, 1, 1, 1, 2, 2, 2, 3},
+	}
+	validate = subject.Validate(context.Background(), peer.ID(senderPID), &pubsub.Message{
+		Message:       pbm,
+		ReceivedFrom:  peer.ID("f01024"), // peer.ID(senderPID),
+		ValidatorData: nil,
+	})
+	if validate != pubsub.ValidationAccept {
+		t.Fatal("Did not receive ValidationAccept")
+	}
+}