diff --git a/chain/gen/gen.go b/chain/gen/gen.go
index 866a75357..8c82895f9 100644
--- a/chain/gen/gen.go
+++ b/chain/gen/gen.go
@@ -526,9 +526,11 @@ func IsRoundWinner(ctx context.Context, ts *types.TipSet, round int64, miner add
 		return nil, xerrors.Errorf("failed to look up miners sector size: %w", err)
 	}
 
+	snum := types.BigDiv(pow.MinerPower, types.NewInt(ssize))
+
 	var winners []sectorbuilder.EPostCandidate
 	for _, c := range candidates {
-		if types.IsTicketWinner(c.PartialTicket[:], ssize, pow.TotalPower) {
+		if types.IsTicketWinner(c.PartialTicket[:], ssize, snum.Uint64(), pow.TotalPower) {
 			winners = append(winners, c)
 		}
 	}
diff --git a/chain/sync.go b/chain/sync.go
index c632c80a0..e594749e9 100644
--- a/chain/sync.go
+++ b/chain/sync.go
@@ -501,7 +501,7 @@ func (syncer *Syncer) ValidateBlock(ctx context.Context, b *types.FullBlock) err
 			return xerrors.Errorf("received block was from miner slashed at height %d", slashedAt)
 		}
 
-		_, tpow, err := stmgr.GetPower(ctx, syncer.sm, baseTs, h.Miner)
+		mpow, tpow, err := stmgr.GetPower(ctx, syncer.sm, baseTs, h.Miner)
 		if err != nil {
 			return xerrors.Errorf("failed getting power: %w", err)
 		}
@@ -511,8 +511,10 @@ func (syncer *Syncer) ValidateBlock(ctx context.Context, b *types.FullBlock) err
 			return xerrors.Errorf("failed to get sector size for block miner: %w", err)
 		}
 
+		snum := types.BigDiv(mpow, types.NewInt(ssize))
+
 		for _, t := range h.EPostProof.Candidates {
-			if !types.IsTicketWinner(t.Partial, ssize, tpow) {
+			if !types.IsTicketWinner(t.Partial, ssize, snum.Uint64(), tpow) {
 				return xerrors.Errorf("miner created a block but was not a winner")
 			}
 		}
diff --git a/chain/types/blockheader.go b/chain/types/blockheader.go
index 7ba5ef436..e44ca54b4 100644
--- a/chain/types/blockheader.go
+++ b/chain/types/blockheader.go
@@ -174,9 +174,9 @@ var blocksPerEpoch = NewInt(build.BlocksPerEpoch)
 
 const sha256bits = 256
 
-func IsTicketWinner(partialTicket []byte, ssizeI uint64, totpow BigInt) bool {
+func IsTicketWinner(partialTicket []byte, ssizeI uint64, snum uint64, totpow BigInt) bool {
 	ssize := NewInt(ssizeI)
-
+	ssampled := ElectionPostChallengeCount(snum)
 	/*
 		Need to check that
 		(h(vrfout) + 1) / (max(h) + 1) <= e * sectorSize / totalPower
@@ -185,23 +185,42 @@ func IsTicketWinner(partialTicket []byte, ssizeI uint64, totpow BigInt) bool {
 		(h(vrfout) + 1) * totalPower <= e * sectorSize * 2^256
 		in 2^256 space, it is equivalent to:
 		h(vrfout) * totalPower < e * sectorSize * 2^256
+
+		Because of SectorChallengeRatioDiv sampling for proofs
+		we need to scale this appropriately.
+
+		Let c = ceil(numSectors/SectorChallengeRatioDiv)
+		(c is the number of tickets a miner requests)
+		Accordingly we check
+		(h(vrfout) + 1) / 2^256 <= e * sectorSize / totalPower * snum / c
+		or
+		h(vrfout) * totalPower * c < e * sectorSize * 2^256 * snum
 	*/
 
 	h := sha256.Sum256(partialTicket)
 
 	lhs := BigFromBytes(h[:]).Int
 	lhs = lhs.Mul(lhs, totpow.Int)
+	lhs = lhs.Mul(lhs, new(big.Int).SetUint64(ssampled))
 
 	// rhs = sectorSize * 2^256
 	// rhs = sectorSize << 256
 	rhs := new(big.Int).Lsh(ssize.Int, sha256bits)
-	rhs = rhs.Mul(rhs, big.NewInt(build.SectorChallengeRatioDiv))
+	rhs = rhs.Mul(rhs, new(big.Int).SetUint64(snum))
 	rhs = rhs.Mul(rhs, blocksPerEpoch.Int)
 
 	// h(vrfout) * totalPower < e * sectorSize * 2^256?
 	return lhs.Cmp(rhs) < 0
 }
 
+func ElectionPostChallengeCount(sectors uint64) uint64 {
+	if sectors == 0 {
+		return 0
+	}
+	// ceil(sectors / build.SectorChallengeRatioDiv)
+	return (sectors-1)/build.SectorChallengeRatioDiv + 1
+}
+
 func (t *Ticket) Equals(ot *Ticket) bool {
 	return bytes.Equal(t.VRFProof, ot.VRFProof)
 }
diff --git a/lib/sectorbuilder/sectorbuilder.go b/lib/sectorbuilder/sectorbuilder.go
index 7a5d744ab..c4fca12d4 100644
--- a/lib/sectorbuilder/sectorbuilder.go
+++ b/lib/sectorbuilder/sectorbuilder.go
@@ -16,6 +16,7 @@ import (
 
 	"github.com/filecoin-project/lotus/build"
 	"github.com/filecoin-project/lotus/chain/address"
+	"github.com/filecoin-project/lotus/chain/types"
 	"github.com/filecoin-project/lotus/node/modules/dtypes"
 )
 
@@ -623,7 +624,7 @@ func (sb *SectorBuilder) GenerateEPostCandidates(sectorInfo SortedPublicSectorIn
 		return nil, err
 	}
 
-	challengeCount := ElectionPostChallengeCount(uint64(len(sectorInfo.Values())))
+	challengeCount := types.ElectionPostChallengeCount(uint64(len(sectorInfo.Values())))
 
 	proverID := addressToProverID(sb.Miner)
 	return sectorbuilder.GenerateCandidates(sb.ssize, proverID, challengeSeed, challengeCount, privsectors)
@@ -674,13 +675,8 @@ func (sb *SectorBuilder) Stop() {
 	close(sb.stopping)
 }
 
-func ElectionPostChallengeCount(sectors uint64) uint64 {
-	// ceil(sectors / build.SectorChallengeRatioDiv)
-	return (sectors + build.SectorChallengeRatioDiv - 1) / build.SectorChallengeRatioDiv
-}
-
 func fallbackPostChallengeCount(sectors uint64) uint64 {
-	challengeCount := ElectionPostChallengeCount(sectors)
+	challengeCount := types.ElectionPostChallengeCount(sectors)
 	if challengeCount > build.MaxFallbackPostChallengeCount {
 		return build.MaxFallbackPostChallengeCount
 	}
diff --git a/lib/sectorbuilder/simple.go b/lib/sectorbuilder/simple.go
index 0c9231092..457c4b2e1 100644
--- a/lib/sectorbuilder/simple.go
+++ b/lib/sectorbuilder/simple.go
@@ -8,6 +8,7 @@ import (
 	"go.opencensus.io/trace"
 
 	"github.com/filecoin-project/lotus/chain/address"
+	"github.com/filecoin-project/lotus/chain/types"
 )
 
 func (sb *SectorBuilder) SectorSize() uint64 {
@@ -36,7 +37,7 @@ func NewSortedPublicSectorInfo(sectors []sectorbuilder.PublicSectorInfo) SortedP
 }
 
 func VerifyElectionPost(ctx context.Context, sectorSize uint64, sectorInfo SortedPublicSectorInfo, challengeSeed []byte, proof []byte, candidates []EPostCandidate, proverID address.Address) (bool, error) {
-	challengeCount := ElectionPostChallengeCount(uint64(len(sectorInfo.Values())))
+	challengeCount := types.ElectionPostChallengeCount(uint64(len(sectorInfo.Values())))
 	return verifyPost(ctx, sectorSize, sectorInfo, challengeCount, challengeSeed, proof, candidates, proverID)
 }