diff --git a/storage/wdpost_changehandler.go b/storage/wdpost_changehandler.go
index 285995757..188d7e93a 100644
--- a/storage/wdpost_changehandler.go
+++ b/storage/wdpost_changehandler.go
@@ -13,7 +13,10 @@ import (
 	"github.com/filecoin-project/lotus/chain/types"
 )
 
-const SubmitConfidence = 4
+const (
+	SubmitConfidence    = 4
+	ChallengeConfidence = 10
+)
 
 type CompleteGeneratePoSTCb func(posts []miner.SubmitWindowedPoStParams, err error)
 type CompleteSubmitPoSTCb func(err error)
@@ -230,7 +233,7 @@ func (p *proveHandler) processHeadChange(ctx context.Context, newTS *types.TipSe
 	}
 
 	// Check if the chain is above the Challenge height for the post window
-	if newTS.Height() < di.Challenge {
+	if newTS.Height() < di.Challenge+ChallengeConfidence {
 		return
 	}
 
diff --git a/storage/wdpost_changehandler_test.go b/storage/wdpost_changehandler_test.go
index 6479c0d7e..bae4f40fd 100644
--- a/storage/wdpost_changehandler_test.go
+++ b/storage/wdpost_changehandler_test.go
@@ -395,7 +395,7 @@ func TestChangeHandlerStartProvingNextDeadline(t *testing.T) {
 
 	// Trigger a head change
 	currentEpoch := abi.ChainEpoch(1)
-	go triggerHeadAdvance(t, s, currentEpoch)
+	go triggerHeadAdvance(t, s, currentEpoch+ChallengeConfidence)
 
 	// Should start proving
 	<-s.ch.proveHdlr.processedHeadChanges
@@ -405,7 +405,7 @@ func TestChangeHandlerStartProvingNextDeadline(t *testing.T) {
 	// Trigger a head change that advances the chain beyond the submit
 	// confidence
 	currentEpoch = 1 + SubmitConfidence
-	go triggerHeadAdvance(t, s, currentEpoch)
+	go triggerHeadAdvance(t, s, currentEpoch+ChallengeConfidence)
 
 	// Should be no change to state yet
 	<-s.ch.proveHdlr.processedHeadChanges
@@ -424,7 +424,7 @@ func TestChangeHandlerStartProvingNextDeadline(t *testing.T) {
 	// the next deadline
 	go func() {
 		di = nextDeadline(di)
-		currentEpoch = di.Challenge
+		currentEpoch = di.Challenge + ChallengeConfidence
 		triggerHeadAdvance(t, s, currentEpoch)
 	}()
 
@@ -446,7 +446,7 @@ func TestChangeHandlerProvingRounds(t *testing.T) {
 	for currentEpoch := abi.ChainEpoch(1); currentEpoch < miner.WPoStChallengeWindow*5; currentEpoch++ {
 		// Trigger a head change
 		di := mock.getDeadline(currentEpoch)
-		go triggerHeadAdvance(t, s, currentEpoch)
+		go triggerHeadAdvance(t, s, currentEpoch+ChallengeConfidence)
 
 		// Wait for prover to process head change
 		<-s.ch.proveHdlr.processedHeadChanges
@@ -913,7 +913,7 @@ func TestChangeHandlerSubmitRevertTwoEpochs(t *testing.T) {
 
 	// Move to the challenge epoch for the next deadline
 	diE2 := nextDeadline(diE1)
-	currentEpoch = diE2.Challenge
+	currentEpoch = diE2.Challenge + ChallengeConfidence
 	go triggerHeadAdvance(t, s, currentEpoch)
 
 	// Should move to submitting state for epoch 1
@@ -1014,7 +1014,7 @@ func TestChangeHandlerSubmitRevertAdvanceLess(t *testing.T) {
 
 	// Move to the challenge epoch for the next deadline
 	diE2 := nextDeadline(diE1)
-	currentEpoch = diE2.Challenge
+	currentEpoch = diE2.Challenge + ChallengeConfidence
 	go triggerHeadAdvance(t, s, currentEpoch)
 
 	// Should move to submitting state for epoch 1
diff --git a/storage/wdpost_run.go b/storage/wdpost_run.go
index 2690069d4..ea4d110de 100644
--- a/storage/wdpost_run.go
+++ b/storage/wdpost_run.go
@@ -600,9 +600,23 @@ func (s *WindowPoStScheduler) runPost(ctx context.Context, di dline.Info, ts *ty
 					return nil, xerrors.Errorf("received no proofs back from generate window post")
 				}
 
+				headTs, err := s.api.ChainHead(ctx)
+				if err != nil {
+					return nil, xerrors.Errorf("getting current head: %w", err)
+				}
+
+				checkRand, err := s.api.ChainGetRandomnessFromBeacon(ctx, headTs.Key(), crypto.DomainSeparationTag_WindowedPoStChallengeSeed, di.Challenge, buf.Bytes())
+				if err != nil {
+					return nil, xerrors.Errorf("failed to get chain randomness from beacon for window post (ts=%d; deadline=%d): %w", ts.Height(), di, err)
+				}
+
+				if !bytes.Equal(checkRand, rand) {
+					log.Warnw("windowpost randomness changed", "old", rand, "new", checkRand, "ts-height", ts.Height(), "challenge-height", di.Challenge, "tsk", ts.Key())
+				}
+
 				// If we generated an incorrect proof, try again.
 				if correct, err := s.verifier.VerifyWindowPoSt(ctx, proof.WindowPoStVerifyInfo{
-					Randomness:        abi.PoStRandomness(rand),
+					Randomness:        abi.PoStRandomness(checkRand),
 					Proofs:            postOut,
 					ChallengedSectors: sinfos,
 					Prover:            abi.ActorID(mid),
diff --git a/storage/wdpost_run_test.go b/storage/wdpost_run_test.go
index 80bd8d3fb..4bf30e3e9 100644
--- a/storage/wdpost_run_test.go
+++ b/storage/wdpost_run_test.go
@@ -350,7 +350,7 @@ func (m *mockStorageMinerAPI) GasEstimateMessageGas(ctx context.Context, message
 }
 
 func (m *mockStorageMinerAPI) ChainHead(ctx context.Context) (*types.TipSet, error) {
-	panic("implement me")
+	return nil, nil
 }
 
 func (m *mockStorageMinerAPI) ChainNotify(ctx context.Context) (<-chan []*api.HeadChange, error) {