diff --git a/beacon-chain/blockchain/testing/mock.go b/beacon-chain/blockchain/testing/mock.go
index a9fd6684f..e662defbb 100644
--- a/beacon-chain/blockchain/testing/mock.go
+++ b/beacon-chain/blockchain/testing/mock.go
@@ -46,6 +46,7 @@ type ChainService struct {
 	opNotifier                  opfeed.Notifier
 	ValidAttestation            bool
 	ForkChoiceStore             *protoarray.Store
+	VerifyBlkDescendantErr      error
 }
 
 // StateNotifier mocks the same method in the chain service.
@@ -350,5 +351,5 @@ func (ms *ChainService) HeadGenesisValidatorRoot() [32]byte {
 
 // VerifyBlkDescendant mocks VerifyBlkDescendant and always returns nil.
 func (ms *ChainService) VerifyBlkDescendant(ctx context.Context, root [32]byte) error {
-	return nil
+	return ms.VerifyBlkDescendantErr
 }
diff --git a/beacon-chain/sync/validate_beacon_blocks.go b/beacon-chain/sync/validate_beacon_blocks.go
index 02d06bef0..aff11c4e6 100644
--- a/beacon-chain/sync/validate_beacon_blocks.go
+++ b/beacon-chain/sync/validate_beacon_blocks.go
@@ -110,6 +110,11 @@ func (s *Service) validateBeaconBlockPubSub(ctx context.Context, pid peer.ID, ms
 		return pubsub.ValidationIgnore
 	}
 
+	if err := s.chain.VerifyBlkDescendant(ctx, bytesutil.ToBytes32(blk.Block.ParentRoot)); err != nil {
+		log.WithError(err).Warn("Rejecting block")
+		return pubsub.ValidationReject
+	}
+
 	hasStateSummaryDB := s.db.HasStateSummary(ctx, bytesutil.ToBytes32(blk.Block.ParentRoot))
 	hasStateSummaryCache := s.stateSummaryCache.Has(bytesutil.ToBytes32(blk.Block.ParentRoot))
 	if !hasStateSummaryDB && !hasStateSummaryCache {
diff --git a/beacon-chain/sync/validate_beacon_blocks_test.go b/beacon-chain/sync/validate_beacon_blocks_test.go
index 2739b50ac..d58adce08 100644
--- a/beacon-chain/sync/validate_beacon_blocks_test.go
+++ b/beacon-chain/sync/validate_beacon_blocks_test.go
@@ -3,6 +3,7 @@ package sync
 import (
 	"bytes"
 	"context"
+	"errors"
 	"reflect"
 	"testing"
 	"time"
@@ -632,3 +633,96 @@ func TestValidateBeaconBlockPubSub_FilterByFinalizedEpoch(t *testing.T) {
 	r.validateBeaconBlockPubSub(context.Background(), "", m)
 	testutil.AssertLogsDoNotContain(t, hook, "Block slot older/equal than last finalized epoch start slot, rejecting itt")
 }
+
+func TestValidateBeaconBlockPubSub_ParentNotFinalizedDescendant(t *testing.T) {
+	hook := logTest.NewGlobal()
+	db, stateSummaryCache := dbtest.SetupDB(t)
+	p := p2ptest.NewTestP2P(t)
+	ctx := context.Background()
+	beaconState, privKeys := testutil.DeterministicGenesisState(t, 100)
+	parentBlock := &ethpb.SignedBeaconBlock{
+		Block: &ethpb.BeaconBlock{
+			ProposerIndex: 0,
+			Slot:          0,
+		},
+	}
+	if err := db.SaveBlock(ctx, parentBlock); err != nil {
+		t.Fatal(err)
+	}
+	bRoot, err := stateutil.BlockRoot(parentBlock.Block)
+	if err := db.SaveState(ctx, beaconState, bRoot); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.SaveStateSummary(ctx, &pb.StateSummary{
+		Root: bRoot[:],
+	}); err != nil {
+		t.Fatal(err)
+	}
+	copied := beaconState.Copy()
+	if err := copied.SetSlot(1); err != nil {
+		t.Fatal(err)
+	}
+	proposerIdx, err := helpers.BeaconProposerIndex(copied)
+	if err != nil {
+		t.Fatal(err)
+	}
+	msg := &ethpb.SignedBeaconBlock{
+		Block: &ethpb.BeaconBlock{
+			ProposerIndex: proposerIdx,
+			Slot:          1,
+			ParentRoot:    bRoot[:],
+		},
+	}
+
+	domain, err := helpers.Domain(beaconState.Fork(), 0, params.BeaconConfig().DomainBeaconProposer, beaconState.GenesisValidatorRoot())
+	if err != nil {
+		t.Fatal(err)
+	}
+	signingRoot, err := helpers.ComputeSigningRoot(msg.Block, domain)
+	if err != nil {
+		t.Error(err)
+	}
+	blockSig := privKeys[proposerIdx].Sign(signingRoot[:]).Marshal()
+	msg.Signature = blockSig[:]
+
+	c, err := lru.New(10)
+	if err != nil {
+		t.Fatal(err)
+	}
+	stateGen := stategen.New(db, stateSummaryCache)
+	chainService := &mock.ChainService{Genesis: time.Unix(time.Now().Unix()-int64(params.BeaconConfig().SecondsPerSlot), 0),
+		State: beaconState,
+		FinalizedCheckPoint: &ethpb.Checkpoint{
+			Epoch: 0,
+		},
+		VerifyBlkDescendantErr: errors.New("not part of finalized chain"),
+	}
+	r := &Service{
+		db:                  db,
+		p2p:                 p,
+		initialSync:         &mockSync.Sync{IsSyncing: false},
+		chain:               chainService,
+		blockNotifier:       chainService.BlockNotifier(),
+		seenBlockCache:      c,
+		slotToPendingBlocks: make(map[uint64]*ethpb.SignedBeaconBlock),
+		seenPendingBlocks:   make(map[[32]byte]bool),
+		stateSummaryCache:   stateSummaryCache,
+		stateGen:            stateGen,
+	}
+	buf := new(bytes.Buffer)
+	if _, err := p.Encoding().EncodeGossip(buf, msg); err != nil {
+		t.Fatal(err)
+	}
+	m := &pubsub.Message{
+		Message: &pubsubpb.Message{
+			Data: buf.Bytes(),
+			TopicIDs: []string{
+				p2p.GossipTypeMapping[reflect.TypeOf(msg)],
+			},
+		},
+	}
+	if res := r.validateBeaconBlockPubSub(ctx, "", m); res != pubsub.ValidationReject {
+		t.Error("Wrong validation result returned")
+	}
+	testutil.AssertLogsContain(t, hook, "not part of finalized chain")
+}