diff --git a/beacon-chain/sync/subscriber_beacon_aggregate_proof.go b/beacon-chain/sync/subscriber_beacon_aggregate_proof.go
index 6bea5d9725e7..7d2d81f1cd14 100644
--- a/beacon-chain/sync/subscriber_beacon_aggregate_proof.go
+++ b/beacon-chain/sync/subscriber_beacon_aggregate_proof.go
@@ -20,7 +20,7 @@ func (r *Service) beaconAggregateProofSubscriber(ctx context.Context, msg proto.
 	if a.Message.Aggregate == nil || a.Message.Aggregate.Data == nil {
 		return errors.New("nil aggregate")
 	}
-	r.setAggregatorIndexSlotSeen(a.Message.Aggregate.Data.Slot, a.Message.AggregatorIndex)
+	r.setAggregatorIndexEpochSeen(a.Message.Aggregate.Data.Target.Epoch, a.Message.AggregatorIndex)
 
 	return r.attPool.SaveAggregatedAttestation(a.Message.Aggregate)
 }
diff --git a/beacon-chain/sync/subscriber_beacon_aggregate_proof_test.go b/beacon-chain/sync/subscriber_beacon_aggregate_proof_test.go
index 436cb41730c1..08b21547a34c 100644
--- a/beacon-chain/sync/subscriber_beacon_aggregate_proof_test.go
+++ b/beacon-chain/sync/subscriber_beacon_aggregate_proof_test.go
@@ -21,7 +21,7 @@ func TestBeaconAggregateProofSubscriber_CanSave(t *testing.T) {
 		seenAttestationCache: c,
 	}
 
-	a := &ethpb.SignedAggregateAttestationAndProof{Message: &ethpb.AggregateAttestationAndProof{Aggregate: &ethpb.Attestation{Data: &ethpb.AttestationData{}, AggregationBits: bitfield.Bitlist{0x07}}, AggregatorIndex: 100}}
+	a := &ethpb.SignedAggregateAttestationAndProof{Message: &ethpb.AggregateAttestationAndProof{Aggregate: &ethpb.Attestation{Data: &ethpb.AttestationData{Target: &ethpb.Checkpoint{}}, AggregationBits: bitfield.Bitlist{0x07}}, AggregatorIndex: 100}}
 	if err := r.beaconAggregateProofSubscriber(context.Background(), a); err != nil {
 		t.Fatal(err)
 	}
diff --git a/beacon-chain/sync/validate_aggregate_proof.go b/beacon-chain/sync/validate_aggregate_proof.go
index 167650d980b9..d3427727ab30 100644
--- a/beacon-chain/sync/validate_aggregate_proof.go
+++ b/beacon-chain/sync/validate_aggregate_proof.go
@@ -53,7 +53,7 @@ func (r *Service) validateAggregateAndProof(ctx context.Context, pid peer.ID, ms
 		return false
 	}
 	// Verify this is the first aggregate received from the aggregator with index and slot.
-	if r.hasSeenAggregatorIndexSlot(m.Message.Aggregate.Data.Slot, m.Message.AggregatorIndex) {
+	if r.hasSeenAggregatorIndexEpoch(m.Message.Aggregate.Data.Target.Epoch, m.Message.AggregatorIndex) {
 		return false
 	}
 
@@ -74,7 +74,7 @@ func (r *Service) validateAggregateAndProof(ctx context.Context, pid peer.ID, ms
 		return false
 	}
 
-	r.setAggregatorIndexSlotSeen(m.Message.Aggregate.Data.Slot, m.Message.AggregatorIndex)
+	r.setAggregatorIndexEpochSeen(m.Message.Aggregate.Data.Target.Epoch, m.Message.AggregatorIndex)
 
 	msg.ValidatorData = m
 
@@ -150,20 +150,20 @@ func (r *Service) validateBlockInAttestation(ctx context.Context, s *ethpb.Signe
 	return true
 }
 
-// Returns true if the node has received aggregate for the aggregator with index and slot.
-func (r *Service) hasSeenAggregatorIndexSlot(slot uint64, aggregatorIndex uint64) bool {
+// Returns true if the node has received aggregate for the aggregator with index and target epoch.
+func (r *Service) hasSeenAggregatorIndexEpoch(epoch uint64, aggregatorIndex uint64) bool {
 	r.seenAttestationLock.RLock()
 	defer r.seenAttestationLock.RUnlock()
-	b := append(bytesutil.Bytes32(slot), bytesutil.Bytes32(aggregatorIndex)...)
+	b := append(bytesutil.Bytes32(epoch), bytesutil.Bytes32(aggregatorIndex)...)
 	_, seen := r.seenAttestationCache.Get(string(b))
 	return seen
 }
 
-// Set aggregate's aggregator index slot as seen.
-func (r *Service) setAggregatorIndexSlotSeen(slot uint64, aggregatorIndex uint64) {
+// Set aggregate's aggregator index target epoch as seen.
+func (r *Service) setAggregatorIndexEpochSeen(epoch uint64, aggregatorIndex uint64) {
 	r.seenAttestationLock.Lock()
 	defer r.seenAttestationLock.Unlock()
-	b := append(bytesutil.Bytes32(slot), bytesutil.Bytes32(aggregatorIndex)...)
+	b := append(bytesutil.Bytes32(epoch), bytesutil.Bytes32(aggregatorIndex)...)
 	r.seenAttestationCache.Add(string(b), true)
 }
 
diff --git a/beacon-chain/sync/validate_aggregate_proof_test.go b/beacon-chain/sync/validate_aggregate_proof_test.go
index bbfad31971dc..bd09b18fffed 100644
--- a/beacon-chain/sync/validate_aggregate_proof_test.go
+++ b/beacon-chain/sync/validate_aggregate_proof_test.go
@@ -468,7 +468,7 @@ func TestValidateAggregateAndProofWithNewStateMgmt_CanValidate(t *testing.T) {
 	}
 }
 
-func TestVerifyIndexInCommittee_SeenAggregatorSlot(t *testing.T) {
+func TestVerifyIndexInCommittee_SeenAggregatorEpoch(t *testing.T) {
 	db := dbtest.SetupDB(t)
 	defer dbtest.TeardownDB(t, db)
 	p := p2ptest.NewTestP2P(t)
@@ -590,6 +590,22 @@ func TestVerifyIndexInCommittee_SeenAggregatorSlot(t *testing.T) {
 	if !r.validateAggregateAndProof(context.Background(), "", msg) {
 		t.Fatal("Validated status is false")
 	}
+
+	// Should fail with another attestation in the same epoch.
+	signedAggregateAndProof.Message.Aggregate.Data.Slot++
+	buf = new(bytes.Buffer)
+	if _, err := p.Encoding().Encode(buf, signedAggregateAndProof); err != nil {
+		t.Fatal(err)
+	}
+	msg = &pubsub.Message{
+		Message: &pubsubpb.Message{
+			Data: buf.Bytes(),
+			TopicIDs: []string{
+				p2p.GossipTypeMapping[reflect.TypeOf(signedAggregateAndProof)],
+			},
+		},
+	}
+
 	time.Sleep(10 * time.Millisecond) // Wait for cached value to pass through buffers.
 	if r.validateAggregateAndProof(context.Background(), "", msg) {
 		t.Fatal("Validated status is true")