diff --git a/chain/gen/gen.go b/chain/gen/gen.go
index 27feaeaaa0d..319b7ac2946 100644
--- a/chain/gen/gen.go
+++ b/chain/gen/gen.go
@@ -75,9 +75,10 @@ type ChainGen struct {
 
 	w *wallet.LocalWallet
 
-	eppProvs    map[address.Address]WinningPoStProver
-	Miners      []address.Address
-	receivers   []address.Address
+	eppProvs  map[address.Address]WinningPoStProver
+	Miners    []address.Address
+	receivers []address.Address
+	// a SecP address
 	banker      address.Address
 	bankerNonce uint64
 
@@ -110,7 +111,7 @@ var DefaultRemainderAccountActor = genesis.Actor{
 	Meta:    remAccMeta.ActorMeta(),
 }
 
-func NewGeneratorWithSectors(numSectors int) (*ChainGen, error) {
+func NewGeneratorWithSectorsAndUpgradeSchedule(numSectors int, us stmgr.UpgradeSchedule) (*ChainGen, error) {
 	j := journal.NilJournal()
 	// TODO: we really shouldn't modify a global variable here.
 	policy.SetSupportedProofTypes(abi.RegisteredSealProof_StackedDrg2KiBV1)
@@ -244,7 +245,10 @@ func NewGeneratorWithSectors(numSectors int) (*ChainGen, error) {
 		mgen[genesis2.MinerAddress(uint64(i))] = &wppProvider{}
 	}
 
-	sm := stmgr.NewStateManager(cs)
+	sm, err := stmgr.NewStateManagerWithUpgradeSchedule(cs, us)
+	if err != nil {
+		return nil, xerrors.Errorf("initing stmgr: %w", err)
+	}
 
 	miners := []address.Address{maddr1, maddr2}
 
@@ -282,6 +286,14 @@ func NewGenerator() (*ChainGen, error) {
 	return NewGeneratorWithSectors(1)
 }
 
+func NewGeneratorWithSectors(numSectors int) (*ChainGen, error) {
+	return NewGeneratorWithSectorsAndUpgradeSchedule(numSectors, stmgr.DefaultUpgradeSchedule())
+}
+
+func NewGeneratorWithUpgradeSchedule(us stmgr.UpgradeSchedule) (*ChainGen, error) {
+	return NewGeneratorWithSectorsAndUpgradeSchedule(1, us)
+}
+
 func (cg *ChainGen) StateManager() *stmgr.StateManager {
 	return cg.sm
 }
@@ -384,7 +396,7 @@ type MinedTipSet struct {
 }
 
 func (cg *ChainGen) NextTipSet() (*MinedTipSet, error) {
-	mts, err := cg.NextTipSetFromMiners(cg.CurTipset.TipSet(), cg.Miners)
+	mts, err := cg.NextTipSetFromMiners(cg.CurTipset.TipSet(), cg.Miners, 0)
 	if err != nil {
 		return nil, err
 	}
@@ -397,7 +409,7 @@ func (cg *ChainGen) SetWinningPoStProver(m address.Address, wpp WinningPoStProve
 	cg.eppProvs[m] = wpp
 }
 
-func (cg *ChainGen) NextTipSetFromMiners(base *types.TipSet, miners []address.Address) (*MinedTipSet, error) {
+func (cg *ChainGen) NextTipSetFromMiners(base *types.TipSet, miners []address.Address, nulls abi.ChainEpoch) (*MinedTipSet, error) {
 	ms, err := cg.GetMessages(cg)
 	if err != nil {
 		return nil, xerrors.Errorf("get random messages: %w", err)
@@ -408,21 +420,23 @@ func (cg *ChainGen) NextTipSetFromMiners(base *types.TipSet, miners []address.Ad
 		msgs[i] = ms
 	}
 
-	fts, err := cg.NextTipSetFromMinersWithMessages(base, miners, msgs)
+	fts, err := cg.NextTipSetFromMinersWithMessagesAndNulls(base, miners, msgs, nulls)
 	if err != nil {
 		return nil, err
 	}
 
+	cg.CurTipset = fts
+
 	return &MinedTipSet{
 		TipSet:   fts,
 		Messages: ms,
 	}, nil
 }
 
-func (cg *ChainGen) NextTipSetFromMinersWithMessages(base *types.TipSet, miners []address.Address, msgs [][]*types.SignedMessage) (*store.FullTipSet, error) {
+func (cg *ChainGen) NextTipSetFromMinersWithMessagesAndNulls(base *types.TipSet, miners []address.Address, msgs [][]*types.SignedMessage, nulls abi.ChainEpoch) (*store.FullTipSet, error) {
 	var blks []*types.FullBlock
 
-	for round := base.Height() + 1; len(blks) == 0; round++ {
+	for round := base.Height() + nulls + 1; len(blks) == 0; round++ {
 		for mi, m := range miners {
 			bvals, et, ticket, err := cg.nextBlockProof(context.TODO(), base, m, round)
 			if err != nil {
@@ -455,6 +469,8 @@ func (cg *ChainGen) NextTipSetFromMinersWithMessages(base *types.TipSet, miners
 		return nil, err
 	}
 
+	cg.CurTipset = fts
+
 	return fts, nil
 }
 
@@ -574,7 +590,7 @@ func (mca mca) ChainGetRandomnessFromTickets(ctx context.Context, tsk types.TipS
 		return nil, xerrors.Errorf("loading tipset key: %w", err)
 	}
 
-	return mca.sm.ChainStore().GetChainRandomness(ctx, pts.Cids(), personalization, randEpoch, entropy)
+	return mca.sm.ChainStore().GetChainRandomnessLookingBack(ctx, pts.Cids(), personalization, randEpoch, entropy)
 }
 
 func (mca mca) ChainGetRandomnessFromBeacon(ctx context.Context, tsk types.TipSetKey, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) (abi.Randomness, error) {
@@ -583,7 +599,7 @@ func (mca mca) ChainGetRandomnessFromBeacon(ctx context.Context, tsk types.TipSe
 		return nil, xerrors.Errorf("loading tipset key: %w", err)
 	}
 
-	return mca.sm.ChainStore().GetBeaconRandomness(ctx, pts.Cids(), personalization, randEpoch, entropy)
+	return mca.sm.ChainStore().GetBeaconRandomnessLookingBack(ctx, pts.Cids(), personalization, randEpoch, entropy)
 }
 
 func (mca mca) MinerGetBaseInfo(ctx context.Context, maddr address.Address, epoch abi.ChainEpoch, tsk types.TipSetKey) (*api.MiningBaseInfo, error) {
diff --git a/chain/gen/genesis/miners.go b/chain/gen/genesis/miners.go
index be33560e564..86fd1681222 100644
--- a/chain/gen/genesis/miners.go
+++ b/chain/gen/genesis/miners.go
@@ -335,13 +335,25 @@ func SetupStorageMiners(ctx context.Context, cs *store.ChainStore, sroot cid.Cid
 // TODO: copied from actors test harness, deduplicate or remove from here
 type fakeRand struct{}
 
-func (fr *fakeRand) GetChainRandomness(ctx context.Context, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (fr *fakeRand) GetChainRandomnessLookingForward(ctx context.Context, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) ([]byte, error) {
 	out := make([]byte, 32)
 	_, _ = rand.New(rand.NewSource(int64(randEpoch * 1000))).Read(out) //nolint
 	return out, nil
 }
 
-func (fr *fakeRand) GetBeaconRandomness(ctx context.Context, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (fr *fakeRand) GetChainRandomnessLookingBack(ctx context.Context, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	out := make([]byte, 32)
+	_, _ = rand.New(rand.NewSource(int64(randEpoch * 1000))).Read(out) //nolint
+	return out, nil
+}
+
+func (fr *fakeRand) GetBeaconRandomnessLookingForward(ctx context.Context, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	out := make([]byte, 32)
+	_, _ = rand.New(rand.NewSource(int64(randEpoch))).Read(out) //nolint
+	return out, nil
+}
+
+func (fr *fakeRand) GetBeaconRandomnessLookingBack(ctx context.Context, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) ([]byte, error) {
 	out := make([]byte, 32)
 	_, _ = rand.New(rand.NewSource(int64(randEpoch))).Read(out) //nolint
 	return out, nil
diff --git a/chain/store/index.go b/chain/store/index.go
index a9da994af9d..324fb7a633a 100644
--- a/chain/store/index.go
+++ b/chain/store/index.go
@@ -107,6 +107,9 @@ func (ci *ChainIndex) fillCache(tsk types.TipSetKey) (*lbEntry, error) {
 	}
 
 	rheight -= ci.skipLength
+	if rheight < 0 {
+		rheight = 0
+	}
 
 	var skipTarget *types.TipSet
 	if parent.Height() < rheight {
diff --git a/chain/store/store.go b/chain/store/store.go
index 7ebe31ec4bf..dfde93fc73d 100644
--- a/chain/store/store.go
+++ b/chain/store/store.go
@@ -1280,7 +1280,15 @@ func DrawRandomness(rbase []byte, pers crypto.DomainSeparationTag, round abi.Cha
 	return h.Sum(nil), nil
 }
 
-func (cs *ChainStore) GetBeaconRandomness(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (cs *ChainStore) GetBeaconRandomnessLookingBack(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cs.GetBeaconRandomness(ctx, blks, pers, round, entropy, true)
+}
+
+func (cs *ChainStore) GetBeaconRandomnessLookingForward(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cs.GetBeaconRandomness(ctx, blks, pers, round, entropy, false)
+}
+
+func (cs *ChainStore) GetBeaconRandomness(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte, lookback bool) ([]byte, error) {
 	_, span := trace.StartSpan(ctx, "store.GetBeaconRandomness")
 	defer span.End()
 	span.AddAttributes(trace.Int64Attribute("round", int64(round)))
@@ -1299,7 +1307,7 @@ func (cs *ChainStore) GetBeaconRandomness(ctx context.Context, blks []cid.Cid, p
 		searchHeight = 0
 	}
 
-	randTs, err := cs.GetTipsetByHeight(ctx, searchHeight, ts, true)
+	randTs, err := cs.GetTipsetByHeight(ctx, searchHeight, ts, lookback)
 	if err != nil {
 		return nil, err
 	}
@@ -1314,7 +1322,15 @@ func (cs *ChainStore) GetBeaconRandomness(ctx context.Context, blks []cid.Cid, p
 	return DrawRandomness(be.Data, pers, round, entropy)
 }
 
-func (cs *ChainStore) GetChainRandomness(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (cs *ChainStore) GetChainRandomnessLookingBack(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cs.GetChainRandomness(ctx, blks, pers, round, entropy, true)
+}
+
+func (cs *ChainStore) GetChainRandomnessLookingForward(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cs.GetChainRandomness(ctx, blks, pers, round, entropy, false)
+}
+
+func (cs *ChainStore) GetChainRandomness(ctx context.Context, blks []cid.Cid, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte, lookback bool) ([]byte, error) {
 	_, span := trace.StartSpan(ctx, "store.GetChainRandomness")
 	defer span.End()
 	span.AddAttributes(trace.Int64Attribute("round", int64(round)))
@@ -1333,7 +1349,7 @@ func (cs *ChainStore) GetChainRandomness(ctx context.Context, blks []cid.Cid, pe
 		searchHeight = 0
 	}
 
-	randTs, err := cs.GetTipsetByHeight(ctx, searchHeight, ts, true)
+	randTs, err := cs.GetTipsetByHeight(ctx, searchHeight, ts, lookback)
 	if err != nil {
 		return nil, err
 	}
@@ -1608,12 +1624,20 @@ func NewChainRand(cs *ChainStore, blks []cid.Cid) vm.Rand {
 	}
 }
 
-func (cr *chainRand) GetChainRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
-	return cr.cs.GetChainRandomness(ctx, cr.blks, pers, round, entropy)
+func (cr *chainRand) GetChainRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cr.cs.GetChainRandomnessLookingBack(ctx, cr.blks, pers, round, entropy)
+}
+
+func (cr *chainRand) GetChainRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cr.cs.GetChainRandomnessLookingForward(ctx, cr.blks, pers, round, entropy)
+}
+
+func (cr *chainRand) GetBeaconRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cr.cs.GetBeaconRandomnessLookingBack(ctx, cr.blks, pers, round, entropy)
 }
 
-func (cr *chainRand) GetBeaconRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
-	return cr.cs.GetBeaconRandomness(ctx, cr.blks, pers, round, entropy)
+func (cr *chainRand) GetBeaconRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return cr.cs.GetBeaconRandomnessLookingForward(ctx, cr.blks, pers, round, entropy)
 }
 
 func (cs *ChainStore) GetTipSetFromKey(tsk types.TipSetKey) (*types.TipSet, error) {
diff --git a/chain/store/store_test.go b/chain/store/store_test.go
index 51e2e08d0c9..62a0430e301 100644
--- a/chain/store/store_test.go
+++ b/chain/store/store_test.go
@@ -76,7 +76,7 @@ func BenchmarkGetRandomness(b *testing.B) {
 	b.ResetTimer()
 
 	for i := 0; i < b.N; i++ {
-		_, err := cs.GetChainRandomness(context.TODO(), last.Cids(), crypto.DomainSeparationTag_SealRandomness, 500, nil)
+		_, err := cs.GetChainRandomnessLookingBack(context.TODO(), last.Cids(), crypto.DomainSeparationTag_SealRandomness, 500, nil)
 		if err != nil {
 			b.Fatal(err)
 		}
diff --git a/chain/sync_test.go b/chain/sync_test.go
index 9570eda328f..095b224ad4c 100644
--- a/chain/sync_test.go
+++ b/chain/sync_test.go
@@ -7,6 +7,12 @@ import (
 	"testing"
 	"time"
 
+	"github.com/filecoin-project/go-state-types/crypto"
+
+	"github.com/filecoin-project/go-state-types/network"
+
+	"github.com/filecoin-project/lotus/chain/stmgr"
+
 	"github.com/ipfs/go-cid"
 
 	ds "github.com/ipfs/go-datastore"
@@ -101,7 +107,7 @@ func prepSyncTest(t testing.TB, h int) *syncTestUtil {
 		g:  g,
 	}
 
-	tu.addSourceNode(h)
+	tu.addSourceNode(stmgr.DefaultUpgradeSchedule(), h)
 	//tu.checkHeight("source", source, h)
 
 	// separate logs
@@ -110,6 +116,53 @@ func prepSyncTest(t testing.TB, h int) *syncTestUtil {
 	return tu
 }
 
+func prepSyncTestWithV5Height(t testing.TB, h int, v5height abi.ChainEpoch) *syncTestUtil {
+	logging.SetLogLevel("*", "INFO")
+
+	us := stmgr.UpgradeSchedule{{
+		// prepare for upgrade.
+		Network:   network.Version9,
+		Height:    1,
+		Migration: stmgr.UpgradeActorsV2,
+	}, {
+		Network:   network.Version10,
+		Height:    2,
+		Migration: stmgr.UpgradeActorsV3,
+	}, {
+		Network:   network.Version12,
+		Height:    3,
+		Migration: stmgr.UpgradeActorsV4,
+	}, {
+		Network:   network.Version13,
+		Height:    v5height,
+		Migration: stmgr.UpgradeActorsV5,
+	}}
+
+	g, err := gen.NewGeneratorWithUpgradeSchedule(us)
+
+	if err != nil {
+		t.Fatalf("%+v", err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	tu := &syncTestUtil{
+		t:      t,
+		ctx:    ctx,
+		cancel: cancel,
+
+		mn: mocknet.New(ctx),
+		g:  g,
+	}
+
+	tu.addSourceNode(us, h)
+	//tu.checkHeight("source", source, h)
+
+	// separate logs
+	fmt.Println("\x1b[31m///////////////////////////////////////////////////\x1b[39b")
+	return tu
+}
+
 func (tu *syncTestUtil) Shutdown() {
 	tu.cancel()
 }
@@ -174,7 +227,7 @@ func (tu *syncTestUtil) pushTsExpectErr(to int, fts *store.FullTipSet, experr bo
 	}
 }
 
-func (tu *syncTestUtil) mineOnBlock(blk *store.FullTipSet, to int, miners []int, wait, fail bool, msgs [][]*types.SignedMessage) *store.FullTipSet {
+func (tu *syncTestUtil) mineOnBlock(blk *store.FullTipSet, to int, miners []int, wait, fail bool, msgs [][]*types.SignedMessage, nulls abi.ChainEpoch) *store.FullTipSet {
 	if miners == nil {
 		for i := range tu.g.Miners {
 			miners = append(miners, i)
@@ -191,10 +244,10 @@ func (tu *syncTestUtil) mineOnBlock(blk *store.FullTipSet, to int, miners []int,
 	var nts *store.FullTipSet
 	var err error
 	if msgs != nil {
-		nts, err = tu.g.NextTipSetFromMinersWithMessages(blk.TipSet(), maddrs, msgs)
+		nts, err = tu.g.NextTipSetFromMinersWithMessagesAndNulls(blk.TipSet(), maddrs, msgs, 0)
 		require.NoError(tu.t, err)
 	} else {
-		mt, err := tu.g.NextTipSetFromMiners(blk.TipSet(), maddrs)
+		mt, err := tu.g.NextTipSetFromMiners(blk.TipSet(), maddrs, nulls)
 		require.NoError(tu.t, err)
 		nts = mt.TipSet
 	}
@@ -209,11 +262,11 @@ func (tu *syncTestUtil) mineOnBlock(blk *store.FullTipSet, to int, miners []int,
 }
 
 func (tu *syncTestUtil) mineNewBlock(src int, miners []int) {
-	mts := tu.mineOnBlock(tu.g.CurTipset, src, miners, true, false, nil)
+	mts := tu.mineOnBlock(tu.g.CurTipset, src, miners, true, false, nil, 0)
 	tu.g.CurTipset = mts
 }
 
-func (tu *syncTestUtil) addSourceNode(gen int) {
+func (tu *syncTestUtil) addSourceNode(us stmgr.UpgradeSchedule, gen int) {
 	if tu.genesis != nil {
 		tu.t.Fatal("source node already exists")
 	}
@@ -229,6 +282,7 @@ func (tu *syncTestUtil) addSourceNode(gen int) {
 		node.Test(),
 
 		node.Override(new(modules.Genesis), modules.LoadGenesis(genesis)),
+		node.Override(new(stmgr.UpgradeSchedule), us),
 	)
 	require.NoError(tu.t, err)
 	tu.t.Cleanup(func() { _ = stop(context.Background()) })
@@ -442,7 +496,7 @@ func TestSyncBadTimestamp(t *testing.T) {
 	fmt.Println("BASE: ", base.Cids())
 	tu.printHeads()
 
-	a1 := tu.mineOnBlock(base, 0, nil, false, true, nil)
+	a1 := tu.mineOnBlock(base, 0, nil, false, true, nil, 0)
 
 	tu.g.Timestamper = nil
 	require.NoError(t, tu.g.ResyncBankerNonce(a1.TipSet()))
@@ -451,7 +505,7 @@ func TestSyncBadTimestamp(t *testing.T) {
 
 	fmt.Println("After mine bad block!")
 	tu.printHeads()
-	a2 := tu.mineOnBlock(base, 0, nil, true, false, nil)
+	a2 := tu.mineOnBlock(base, 0, nil, true, false, nil, 0)
 
 	tu.waitUntilSync(0, client)
 
@@ -495,7 +549,7 @@ func TestSyncBadWinningPoSt(t *testing.T) {
 	tu.g.SetWinningPoStProver(tu.g.Miners[1], &badWpp{})
 
 	// now ensure that new blocks are not accepted
-	tu.mineOnBlock(base, client, nil, false, true, nil)
+	tu.mineOnBlock(base, client, nil, false, true, nil, 0)
 }
 
 func (tu *syncTestUtil) loadChainToNode(to int) {
@@ -540,16 +594,16 @@ func TestSyncFork(t *testing.T) {
 	fmt.Println("Mining base: ", base.TipSet().Cids(), base.TipSet().Height())
 
 	// The two nodes fork at this point into 'a' and 'b'
-	a1 := tu.mineOnBlock(base, p1, []int{0}, true, false, nil)
-	a := tu.mineOnBlock(a1, p1, []int{0}, true, false, nil)
-	a = tu.mineOnBlock(a, p1, []int{0}, true, false, nil)
+	a1 := tu.mineOnBlock(base, p1, []int{0}, true, false, nil, 0)
+	a := tu.mineOnBlock(a1, p1, []int{0}, true, false, nil, 0)
+	a = tu.mineOnBlock(a, p1, []int{0}, true, false, nil, 0)
 
 	require.NoError(t, tu.g.ResyncBankerNonce(a1.TipSet()))
 	// chain B will now be heaviest
-	b := tu.mineOnBlock(base, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
+	b := tu.mineOnBlock(base, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
 
 	fmt.Println("A: ", a.Cids(), a.TipSet().Height())
 	fmt.Println("B: ", b.Cids(), b.TipSet().Height())
@@ -611,13 +665,13 @@ func TestDuplicateNonce(t *testing.T) {
 		msgs[k] = []*types.SignedMessage{makeMsg(tu.g.Miners[k])}
 	}
 
-	ts1 := tu.mineOnBlock(base, 0, []int{0, 1}, true, false, msgs)
+	ts1 := tu.mineOnBlock(base, 0, []int{0, 1}, true, false, msgs, 0)
 
 	tu.waitUntilSyncTarget(0, ts1.TipSet())
 
 	// mine another tipset
 
-	ts2 := tu.mineOnBlock(ts1, 0, []int{0, 1}, true, false, make([][]*types.SignedMessage, 2))
+	ts2 := tu.mineOnBlock(ts1, 0, []int{0, 1}, true, false, make([][]*types.SignedMessage, 2), 0)
 	tu.waitUntilSyncTarget(0, ts2.TipSet())
 
 	var includedMsg cid.Cid
@@ -668,11 +722,15 @@ func TestBadNonce(t *testing.T) {
 
 	base := tu.g.CurTipset
 
+	// Get the banker from computed tipset state, not the parent.
+	st, _, err := tu.g.StateManager().TipSetState(context.TODO(), base.TipSet())
+	require.NoError(t, err)
+	ba, err := tu.g.StateManager().LoadActorRaw(context.TODO(), tu.g.Banker(), st)
+	require.NoError(t, err)
+
 	// Produce a message from the banker with a bad nonce
 	makeBadMsg := func() *types.SignedMessage {
 
-		ba, err := tu.nds[0].StateGetActor(context.TODO(), tu.g.Banker(), base.TipSet().Key())
-		require.NoError(t, err)
 		msg := types.Message{
 			To:   tu.g.Banker(),
 			From: tu.g.Banker(),
@@ -700,7 +758,7 @@ func TestBadNonce(t *testing.T) {
 	msgs := make([][]*types.SignedMessage, 1)
 	msgs[0] = []*types.SignedMessage{makeBadMsg()}
 
-	tu.mineOnBlock(base, 0, []int{0}, true, true, msgs)
+	tu.mineOnBlock(base, 0, []int{0}, true, true, msgs, 0)
 }
 
 func BenchmarkSyncBasic(b *testing.B) {
@@ -765,19 +823,19 @@ func TestSyncCheckpointHead(t *testing.T) {
 	fmt.Println("Mining base: ", base.TipSet().Cids(), base.TipSet().Height())
 
 	// The two nodes fork at this point into 'a' and 'b'
-	a1 := tu.mineOnBlock(base, p1, []int{0}, true, false, nil)
-	a := tu.mineOnBlock(a1, p1, []int{0}, true, false, nil)
-	a = tu.mineOnBlock(a, p1, []int{0}, true, false, nil)
+	a1 := tu.mineOnBlock(base, p1, []int{0}, true, false, nil, 0)
+	a := tu.mineOnBlock(a1, p1, []int{0}, true, false, nil, 0)
+	a = tu.mineOnBlock(a, p1, []int{0}, true, false, nil, 0)
 
 	tu.waitUntilSyncTarget(p1, a.TipSet())
 	tu.checkpointTs(p1, a.TipSet().Key())
 
 	require.NoError(t, tu.g.ResyncBankerNonce(a1.TipSet()))
 	// chain B will now be heaviest
-	b := tu.mineOnBlock(base, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
+	b := tu.mineOnBlock(base, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
 
 	fmt.Println("A: ", a.Cids(), a.TipSet().Height())
 	fmt.Println("B: ", b.Cids(), b.TipSet().Height())
@@ -807,19 +865,19 @@ func TestSyncCheckpointEarlierThanHead(t *testing.T) {
 	fmt.Println("Mining base: ", base.TipSet().Cids(), base.TipSet().Height())
 
 	// The two nodes fork at this point into 'a' and 'b'
-	a1 := tu.mineOnBlock(base, p1, []int{0}, true, false, nil)
-	a := tu.mineOnBlock(a1, p1, []int{0}, true, false, nil)
-	a = tu.mineOnBlock(a, p1, []int{0}, true, false, nil)
+	a1 := tu.mineOnBlock(base, p1, []int{0}, true, false, nil, 0)
+	a := tu.mineOnBlock(a1, p1, []int{0}, true, false, nil, 0)
+	a = tu.mineOnBlock(a, p1, []int{0}, true, false, nil, 0)
 
 	tu.waitUntilSyncTarget(p1, a.TipSet())
 	tu.checkpointTs(p1, a1.TipSet().Key())
 
 	require.NoError(t, tu.g.ResyncBankerNonce(a1.TipSet()))
 	// chain B will now be heaviest
-	b := tu.mineOnBlock(base, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
-	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil)
+	b := tu.mineOnBlock(base, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
+	b = tu.mineOnBlock(b, p2, []int{1}, true, false, nil, 0)
 
 	fmt.Println("A: ", a.Cids(), a.TipSet().Height())
 	fmt.Println("B: ", b.Cids(), b.TipSet().Height())
@@ -833,3 +891,58 @@ func TestSyncCheckpointEarlierThanHead(t *testing.T) {
 	require.Equal(tu.t, p1Head, a.TipSet())
 	tu.assertBad(p1, b.TipSet())
 }
+
+func TestDrandNull(t *testing.T) {
+	H := 10
+	v5h := abi.ChainEpoch(50)
+	ov5h := build.UpgradeHyperdriveHeight
+	build.UpgradeHyperdriveHeight = v5h
+	tu := prepSyncTestWithV5Height(t, H, v5h)
+
+	entropy := []byte{0, 2, 3, 4}
+	// arbitrarily chosen
+	pers := crypto.DomainSeparationTag_WinningPoStChallengeSeed
+
+	beforeNull := tu.g.CurTipset
+	afterNull := tu.mineOnBlock(beforeNull, 0, nil, false, false, nil, 2)
+	nullHeight := beforeNull.TipSet().Height() + 1
+	if afterNull.TipSet().Height() == nullHeight {
+		t.Fatal("didn't inject nulls as expected")
+	}
+
+	rand, err := tu.nds[0].ChainGetRandomnessFromBeacon(tu.ctx, afterNull.TipSet().Key(), pers, nullHeight, entropy)
+	require.NoError(t, err)
+
+	// calculate the expected randomness based on the beacon BEFORE the null
+	expectedBE := beforeNull.Blocks[0].Header.BeaconEntries
+	expectedRand, err := store.DrawRandomness(expectedBE[len(expectedBE)-1].Data, pers, nullHeight, entropy)
+	require.NoError(t, err)
+
+	require.Equal(t, []byte(rand), expectedRand)
+
+	// zoom zoom to past the v5 upgrade by injecting many many nulls
+	postUpgrade := tu.mineOnBlock(afterNull, 0, nil, false, false, nil, v5h)
+	nv, err := tu.nds[0].StateNetworkVersion(tu.ctx, types.EmptyTSK)
+	require.NoError(t, err)
+	if nv != network.Version13 {
+		t.Fatal("expect to be v13 by now")
+	}
+
+	afterNull = tu.mineOnBlock(postUpgrade, 0, nil, false, false, nil, 2)
+	nullHeight = postUpgrade.TipSet().Height() + 1
+	if afterNull.TipSet().Height() == nullHeight {
+		t.Fatal("didn't inject nulls as expected")
+	}
+
+	rand, err = tu.nds[0].ChainGetRandomnessFromBeacon(tu.ctx, afterNull.TipSet().Key(), pers, nullHeight, entropy)
+	require.NoError(t, err)
+
+	// calculate the expected randomness based on the beacon AFTER the null
+	expectedBE = afterNull.Blocks[0].Header.BeaconEntries
+	expectedRand, err = store.DrawRandomness(expectedBE[len(expectedBE)-1].Data, pers, nullHeight, entropy)
+	require.NoError(t, err)
+
+	require.Equal(t, []byte(rand), expectedRand)
+	build.UpgradeHyperdriveHeight = ov5h
+
+}
diff --git a/chain/vm/runtime.go b/chain/vm/runtime.go
index a3e2f293f68..f89bd9f409e 100644
--- a/chain/vm/runtime.go
+++ b/chain/vm/runtime.go
@@ -208,17 +208,31 @@ func (rt *Runtime) GetActorCodeCID(addr address.Address) (ret cid.Cid, ok bool)
 }
 
 func (rt *Runtime) GetRandomnessFromTickets(personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) abi.Randomness {
-	res, err := rt.vm.rand.GetChainRandomness(rt.ctx, personalization, randEpoch, entropy)
+	var err error
+	var res []byte
+	if rt.vm.GetNtwkVersion(rt.ctx, randEpoch) >= network.Version13 {
+		res, err = rt.vm.rand.GetChainRandomnessLookingForward(rt.ctx, personalization, randEpoch, entropy)
+	} else {
+		res, err = rt.vm.rand.GetChainRandomnessLookingBack(rt.ctx, personalization, randEpoch, entropy)
+	}
+
 	if err != nil {
-		panic(aerrors.Fatalf("could not get randomness: %s", err))
+		panic(aerrors.Fatalf("could not get ticket randomness: %s", err))
 	}
 	return res
 }
 
 func (rt *Runtime) GetRandomnessFromBeacon(personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) abi.Randomness {
-	res, err := rt.vm.rand.GetBeaconRandomness(rt.ctx, personalization, randEpoch, entropy)
+	var err error
+	var res []byte
+	if rt.vm.GetNtwkVersion(rt.ctx, randEpoch) >= network.Version13 {
+		res, err = rt.vm.rand.GetBeaconRandomnessLookingForward(rt.ctx, personalization, randEpoch, entropy)
+	} else {
+		res, err = rt.vm.rand.GetBeaconRandomnessLookingBack(rt.ctx, personalization, randEpoch, entropy)
+	}
+
 	if err != nil {
-		panic(aerrors.Fatalf("could not get randomness: %s", err))
+		panic(aerrors.Fatalf("could not get beacon randomness: %s", err))
 	}
 	return res
 }
diff --git a/chain/vm/vm.go b/chain/vm/vm.go
index afc74e744f1..88ec93a80f8 100644
--- a/chain/vm/vm.go
+++ b/chain/vm/vm.go
@@ -255,8 +255,10 @@ func NewVM(ctx context.Context, opts *VMOpts) (*VM, error) {
 }
 
 type Rand interface {
-	GetChainRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error)
-	GetBeaconRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error)
+	GetChainRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error)
+	GetChainRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error)
+	GetBeaconRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error)
+	GetBeaconRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error)
 }
 
 type ApplyRet struct {
diff --git a/conformance/rand_fixed.go b/conformance/rand_fixed.go
index d356b53d049..f15910e1d6d 100644
--- a/conformance/rand_fixed.go
+++ b/conformance/rand_fixed.go
@@ -19,10 +19,18 @@ func NewFixedRand() vm.Rand {
 	return &fixedRand{}
 }
 
-func (r *fixedRand) GetChainRandomness(_ context.Context, _ crypto.DomainSeparationTag, _ abi.ChainEpoch, _ []byte) ([]byte, error) {
+func (r *fixedRand) GetChainRandomnessLookingForward(_ context.Context, _ crypto.DomainSeparationTag, _ abi.ChainEpoch, _ []byte) ([]byte, error) {
 	return []byte("i_am_random_____i_am_random_____"), nil // 32 bytes.
 }
 
-func (r *fixedRand) GetBeaconRandomness(_ context.Context, _ crypto.DomainSeparationTag, _ abi.ChainEpoch, _ []byte) ([]byte, error) {
+func (r *fixedRand) GetChainRandomnessLookingBack(_ context.Context, _ crypto.DomainSeparationTag, _ abi.ChainEpoch, _ []byte) ([]byte, error) {
+	return []byte("i_am_random_____i_am_random_____"), nil // 32 bytes.
+}
+
+func (r *fixedRand) GetBeaconRandomnessLookingForward(_ context.Context, _ crypto.DomainSeparationTag, _ abi.ChainEpoch, _ []byte) ([]byte, error) {
+	return []byte("i_am_random_____i_am_random_____"), nil // 32 bytes.
+}
+
+func (r *fixedRand) GetBeaconRandomnessLookingBack(_ context.Context, _ crypto.DomainSeparationTag, _ abi.ChainEpoch, _ []byte) ([]byte, error) {
 	return []byte("i_am_random_____i_am_random_____"), nil // 32 bytes.
 }
diff --git a/conformance/rand_record.go b/conformance/rand_record.go
index 6f6d064dc74..5b4985fefea 100644
--- a/conformance/rand_record.go
+++ b/conformance/rand_record.go
@@ -45,8 +45,17 @@ func (r *RecordingRand) loadHead() {
 	r.head = head.Key()
 }
 
-func (r *RecordingRand) GetChainRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (r *RecordingRand) GetChainRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getChainRandomness(ctx, pers, round, entropy)
+}
+
+func (r *RecordingRand) GetChainRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getChainRandomness(ctx, pers, round, entropy)
+}
+
+func (r *RecordingRand) getChainRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
 	r.once.Do(r.loadHead)
+	// FullNode's ChainGetRandomnessFromTickets handles whether we should be looking forward or back
 	ret, err := r.api.ChainGetRandomnessFromTickets(ctx, r.head, pers, round, entropy)
 	if err != nil {
 		return ret, err
@@ -70,7 +79,15 @@ func (r *RecordingRand) GetChainRandomness(ctx context.Context, pers crypto.Doma
 	return ret, err
 }
 
-func (r *RecordingRand) GetBeaconRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (r *RecordingRand) GetBeaconRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getBeaconRandomness(ctx, pers, round, entropy)
+}
+
+func (r *RecordingRand) GetBeaconRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getBeaconRandomness(ctx, pers, round, entropy)
+}
+
+func (r *RecordingRand) getBeaconRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
 	r.once.Do(r.loadHead)
 	ret, err := r.api.ChainGetRandomnessFromBeacon(ctx, r.head, pers, round, entropy)
 	if err != nil {
diff --git a/conformance/rand_replay.go b/conformance/rand_replay.go
index 1b73e5a08af..faae1d090a7 100644
--- a/conformance/rand_replay.go
+++ b/conformance/rand_replay.go
@@ -43,7 +43,15 @@ func (r *ReplayingRand) match(requested schema.RandomnessRule) ([]byte, bool) {
 	return nil, false
 }
 
-func (r *ReplayingRand) GetChainRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (r *ReplayingRand) GetChainRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getChainRandomness(ctx, pers, round, entropy, false)
+}
+
+func (r *ReplayingRand) GetChainRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getChainRandomness(ctx, pers, round, entropy, true)
+}
+
+func (r *ReplayingRand) getChainRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte, lookback bool) ([]byte, error) {
 	rule := schema.RandomnessRule{
 		Kind:                schema.RandomnessChain,
 		DomainSeparationTag: int64(pers),
@@ -57,10 +65,23 @@ func (r *ReplayingRand) GetChainRandomness(ctx context.Context, pers crypto.Doma
 	}
 
 	r.reporter.Logf("returning fallback chain randomness: dst=%d, epoch=%d, entropy=%x", pers, round, entropy)
-	return r.fallback.GetChainRandomness(ctx, pers, round, entropy)
+
+	if lookback {
+		return r.fallback.GetChainRandomnessLookingBack(ctx, pers, round, entropy)
+	}
+
+	return r.fallback.GetChainRandomnessLookingForward(ctx, pers, round, entropy)
 }
 
-func (r *ReplayingRand) GetBeaconRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+func (r *ReplayingRand) GetBeaconRandomnessLookingForward(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getBeaconRandomness(ctx, pers, round, entropy, false)
+}
+
+func (r *ReplayingRand) GetBeaconRandomnessLookingBack(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte) ([]byte, error) {
+	return r.getBeaconRandomness(ctx, pers, round, entropy, true)
+}
+
+func (r *ReplayingRand) getBeaconRandomness(ctx context.Context, pers crypto.DomainSeparationTag, round abi.ChainEpoch, entropy []byte, lookback bool) ([]byte, error) {
 	rule := schema.RandomnessRule{
 		Kind:                schema.RandomnessBeacon,
 		DomainSeparationTag: int64(pers),
@@ -74,6 +95,10 @@ func (r *ReplayingRand) GetBeaconRandomness(ctx context.Context, pers crypto.Dom
 	}
 
 	r.reporter.Logf("returning fallback beacon randomness: dst=%d, epoch=%d, entropy=%x", pers, round, entropy)
-	return r.fallback.GetBeaconRandomness(ctx, pers, round, entropy)
 
+	if lookback {
+		return r.fallback.GetBeaconRandomnessLookingBack(ctx, pers, round, entropy)
+	}
+
+	return r.fallback.GetBeaconRandomnessLookingForward(ctx, pers, round, entropy)
 }
diff --git a/node/impl/full/chain.go b/node/impl/full/chain.go
index c4593219539..845c0ce60c4 100644
--- a/node/impl/full/chain.go
+++ b/node/impl/full/chain.go
@@ -10,6 +10,8 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/filecoin-project/lotus/build"
+
 	"go.uber.org/fx"
 	"golang.org/x/xerrors"
 
@@ -95,7 +97,12 @@ func (a *ChainAPI) ChainGetRandomnessFromTickets(ctx context.Context, tsk types.
 		return nil, xerrors.Errorf("loading tipset key: %w", err)
 	}
 
-	return a.Chain.GetChainRandomness(ctx, pts.Cids(), personalization, randEpoch, entropy)
+	// Doing this here is slightly nicer than doing it in the chainstore directly, but it's still bad for ChainAPI to reason about network upgrades
+	if randEpoch > build.UpgradeHyperdriveHeight {
+		return a.Chain.GetChainRandomnessLookingForward(ctx, pts.Cids(), personalization, randEpoch, entropy)
+	}
+
+	return a.Chain.GetChainRandomnessLookingBack(ctx, pts.Cids(), personalization, randEpoch, entropy)
 }
 
 func (a *ChainAPI) ChainGetRandomnessFromBeacon(ctx context.Context, tsk types.TipSetKey, personalization crypto.DomainSeparationTag, randEpoch abi.ChainEpoch, entropy []byte) (abi.Randomness, error) {
@@ -104,7 +111,12 @@ func (a *ChainAPI) ChainGetRandomnessFromBeacon(ctx context.Context, tsk types.T
 		return nil, xerrors.Errorf("loading tipset key: %w", err)
 	}
 
-	return a.Chain.GetBeaconRandomness(ctx, pts.Cids(), personalization, randEpoch, entropy)
+	// Doing this here is slightly nicer than doing it in the chainstore directly, but it's still bad for ChainAPI to reason about network upgrades
+	if randEpoch > build.UpgradeHyperdriveHeight {
+		return a.Chain.GetBeaconRandomnessLookingForward(ctx, pts.Cids(), personalization, randEpoch, entropy)
+	}
+
+	return a.Chain.GetBeaconRandomnessLookingBack(ctx, pts.Cids(), personalization, randEpoch, entropy)
 }
 
 func (a *ChainAPI) ChainGetBlock(ctx context.Context, msg cid.Cid) (*types.BlockHeader, error) {