diff --git a/beacon-chain/core/state/transition.go b/beacon-chain/core/state/transition.go
index 2d59a29f70ed..b402f758f779 100644
--- a/beacon-chain/core/state/transition.go
+++ b/beacon-chain/core/state/transition.go
@@ -72,7 +72,7 @@ func ExecuteStateTransition(
 
 	// Execute per epoch transition.
 	if e.CanProcessEpoch(state) {
-		state, err = ProcessEpoch(ctx, state, config)
+		state, err = ProcessEpoch(ctx, state, block, config)
 	}
 	if err != nil {
 		return nil, fmt.Errorf("could not process epoch: %v", err)
@@ -195,7 +195,7 @@ func ProcessBlock(
 // 	 process_crosslink_reward_penalties(state)
 // 	 update_validator_registry(state)
 // 	 final_book_keeping(state)
-func ProcessEpoch(ctx context.Context, state *pb.BeaconState, config *TransitionConfig) (*pb.BeaconState, error) {
+func ProcessEpoch(ctx context.Context, state *pb.BeaconState, block *pb.BeaconBlock, config *TransitionConfig) (*pb.BeaconState, error) {
 	ctx, span := trace.StartSpan(ctx, "beacon-chain.ChainService.state.ProcessEpoch")
 	defer span.End()
 
@@ -400,9 +400,11 @@ func ProcessEpoch(ctx context.Context, state *pb.BeaconState, config *Transition
 	state = e.ProcessPrevSlotShardSeed(state)
 	state = v.ProcessPenaltiesAndExits(state)
 	if e.CanProcessValidatorRegistry(state) {
-		state, err = v.UpdateRegistry(state)
-		if err != nil {
-			return nil, fmt.Errorf("could not update validator registry: %v", err)
+		if block != nil {
+			state, err = v.UpdateRegistry(state)
+			if err != nil {
+				return nil, fmt.Errorf("could not update validator registry: %v", err)
+			}
 		}
 		state, err = e.ProcessCurrSlotShardSeed(state)
 		if err != nil {
diff --git a/beacon-chain/core/state/transition_test.go b/beacon-chain/core/state/transition_test.go
index 70b672f7b589..bd9bc1d72e97 100644
--- a/beacon-chain/core/state/transition_test.go
+++ b/beacon-chain/core/state/transition_test.go
@@ -457,12 +457,83 @@ func TestProcessEpoch_PassesProcessingConditions(t *testing.T) {
 			params.BeaconConfig().LatestSlashedExitLength),
 	}
 
-	_, err := state.ProcessEpoch(context.Background(), newState, state.DefaultConfig())
+	_, err := state.ProcessEpoch(context.Background(), newState, &pb.BeaconBlock{}, state.DefaultConfig())
 	if err != nil {
 		t.Errorf("Expected epoch transition to pass processing conditions: %v", err)
 	}
 }
 
+func TestProcessEpoch_PreventsRegistryUpdateOnNilBlock(t *testing.T) {
+	featureconfig.InitFeatureConfig(&featureconfig.FeatureFlagConfig{
+		EnableCrosslinks: false,
+	})
+	var validatorRegistry []*pb.Validator
+	for i := uint64(0); i < 10; i++ {
+		validatorRegistry = append(validatorRegistry,
+			&pb.Validator{
+				ExitEpoch: params.BeaconConfig().FarFutureEpoch,
+			})
+	}
+	validatorBalances := make([]uint64, len(validatorRegistry))
+	for i := 0; i < len(validatorBalances); i++ {
+		validatorBalances[i] = params.BeaconConfig().MaxDepositAmount
+	}
+
+	var attestations []*pb.PendingAttestation
+	for i := uint64(0); i < params.BeaconConfig().SlotsPerEpoch*2; i++ {
+		attestations = append(attestations, &pb.PendingAttestation{
+			Data: &pb.AttestationData{
+				Slot:                     i + params.BeaconConfig().SlotsPerEpoch + params.BeaconConfig().GenesisSlot,
+				Shard:                    1,
+				JustifiedEpoch:           params.BeaconConfig().GenesisEpoch + 1,
+				JustifiedBlockRootHash32: []byte{0},
+			},
+			InclusionSlot: i + params.BeaconConfig().SlotsPerEpoch + 1 + params.BeaconConfig().GenesisSlot,
+		})
+	}
+
+	var blockRoots [][]byte
+	for i := uint64(0); i < params.BeaconConfig().LatestBlockRootsLength; i++ {
+		blockRoots = append(blockRoots, []byte{byte(i)})
+	}
+
+	var randaoHashes [][]byte
+	for i := uint64(0); i < params.BeaconConfig().SlotsPerEpoch; i++ {
+		randaoHashes = append(randaoHashes, []byte{byte(i)})
+	}
+
+	crosslinkRecord := make([]*pb.Crosslink, 64)
+	newState := &pb.BeaconState{
+		Slot:                   params.BeaconConfig().SlotsPerEpoch + params.BeaconConfig().GenesisSlot + 1,
+		LatestAttestations:     attestations,
+		ValidatorBalances:      validatorBalances,
+		ValidatorRegistry:      validatorRegistry,
+		LatestBlockRootHash32S: blockRoots,
+		LatestCrosslinks:       crosslinkRecord,
+		LatestRandaoMixes:      randaoHashes,
+		LatestIndexRootHash32S: make([][]byte,
+			params.BeaconConfig().LatestActiveIndexRootsLength),
+		LatestSlashedBalances: make([]uint64,
+			params.BeaconConfig().LatestSlashedExitLength),
+		ValidatorRegistryUpdateEpoch: params.BeaconConfig().GenesisEpoch,
+		FinalizedEpoch:               params.BeaconConfig().GenesisEpoch + 1,
+	}
+
+	newState, err := state.ProcessEpoch(context.Background(), newState, nil, state.DefaultConfig())
+	if err != nil {
+		t.Errorf("Expected epoch transition to pass processing conditions: %v", err)
+	}
+	if newState.ValidatorRegistryUpdateEpoch != params.BeaconConfig().GenesisEpoch {
+		t.Errorf(
+			"Expected registry to not have been updated, received update epoch: %v",
+			newState.ValidatorRegistryUpdateEpoch-params.BeaconConfig().GenesisEpoch,
+		)
+	}
+	featureconfig.InitFeatureConfig(&featureconfig.FeatureFlagConfig{
+		EnableCrosslinks: true,
+	})
+}
+
 func TestProcessEpoch_InactiveConditions(t *testing.T) {
 	defaultBalance := params.BeaconConfig().MaxDepositAmount
 
@@ -517,7 +588,7 @@ func TestProcessEpoch_InactiveConditions(t *testing.T) {
 			params.BeaconConfig().LatestSlashedExitLength),
 	}
 
-	_, err := state.ProcessEpoch(context.Background(), newState, state.DefaultConfig())
+	_, err := state.ProcessEpoch(context.Background(), newState, &pb.BeaconBlock{}, state.DefaultConfig())
 	if err != nil {
 		t.Errorf("Expected epoch transition to pass processing conditions: %v", err)
 	}
@@ -536,7 +607,7 @@ func TestProcessEpoch_CantGetBoundaryAttestation(t *testing.T) {
 		0,
 		newState.Slot-params.BeaconConfig().GenesisSlot,
 	)
-	if _, err := state.ProcessEpoch(context.Background(), newState, state.DefaultConfig()); !strings.Contains(err.Error(), want) {
+	if _, err := state.ProcessEpoch(context.Background(), newState, &pb.BeaconBlock{}, state.DefaultConfig()); !strings.Contains(err.Error(), want) {
 		t.Errorf("Expected: %s, received: %v", want, err)
 	}
 }
@@ -566,7 +637,7 @@ func TestProcessEpoch_CantGetCurrentValidatorIndices(t *testing.T) {
 	}
 
 	wanted := fmt.Sprintf("wanted participants bitfield length %d, got: %d", 0, 1)
-	if _, err := state.ProcessEpoch(context.Background(), newState, state.DefaultConfig()); !strings.Contains(err.Error(), wanted) {
+	if _, err := state.ProcessEpoch(context.Background(), newState, &pb.BeaconBlock{}, state.DefaultConfig()); !strings.Contains(err.Error(), wanted) {
 		t.Errorf("Expected: %s, received: %v", wanted, err)
 	}
 }