diff --git a/ffiwrapper/verifier_cgo.go b/ffiwrapper/verifier_cgo.go
index 60d56dddc..1fecf9598 100644
--- a/ffiwrapper/verifier_cgo.go
+++ b/ffiwrapper/verifier_cgo.go
@@ -15,7 +15,7 @@ import (
 )
 
 func (sb *Sealer) GenerateWinningPoSt(ctx context.Context, minerID abi.ActorID, sectorInfo []abi.SectorInfo, randomness abi.PoStRandomness) ([]abi.PoStProof, error) {
-	randomness[31] = 0                                                                                                                       // TODO: Not correct, fixme
+	randomness[31] &= 0x3f
 	privsectors, skipped, done, err := sb.pubSectorToPriv(ctx, minerID, sectorInfo, nil, abi.RegisteredSealProof.RegisteredWinningPoStProof) // TODO: FAULTS?
 	if err != nil {
 		return nil, err
@@ -29,7 +29,7 @@ func (sb *Sealer) GenerateWinningPoSt(ctx context.Context, minerID abi.ActorID,
 }
 
 func (sb *Sealer) GenerateWindowPoSt(ctx context.Context, minerID abi.ActorID, sectorInfo []abi.SectorInfo, randomness abi.PoStRandomness) ([]abi.PoStProof, []abi.SectorID, error) {
-	randomness[31] = 0 // TODO: Not correct, fixme
+	randomness[31] &= 0x3f
 	privsectors, skipped, done, err := sb.pubSectorToPriv(ctx, minerID, sectorInfo, nil, abi.RegisteredSealProof.RegisteredWindowPoStProof)
 	if err != nil {
 		return nil, nil, xerrors.Errorf("gathering sector info: %w", err)
@@ -98,7 +98,7 @@ func (proofVerifier) VerifySeal(info abi.SealVerifyInfo) (bool, error) {
 }
 
 func (proofVerifier) VerifyWinningPoSt(ctx context.Context, info abi.WinningPoStVerifyInfo) (bool, error) {
-	info.Randomness[31] = 0 // TODO: Not correct, fixme
+	info.Randomness[31] &= 0x3f
 	_, span := trace.StartSpan(ctx, "VerifyWinningPoSt")
 	defer span.End()
 
@@ -106,7 +106,7 @@ func (proofVerifier) VerifyWinningPoSt(ctx context.Context, info abi.WinningPoSt
 }
 
 func (proofVerifier) VerifyWindowPoSt(ctx context.Context, info abi.WindowPoStVerifyInfo) (bool, error) {
-	info.Randomness[31] = 0 // TODO: Not correct, fixme
+	info.Randomness[31] &= 0x3f
 	_, span := trace.StartSpan(ctx, "VerifyWindowPoSt")
 	defer span.End()
 
@@ -114,6 +114,6 @@ func (proofVerifier) VerifyWindowPoSt(ctx context.Context, info abi.WindowPoStVe
 }
 
 func (proofVerifier) GenerateWinningPoStSectorChallenge(ctx context.Context, proofType abi.RegisteredPoStProof, minerID abi.ActorID, randomness abi.PoStRandomness, eligibleSectorCount uint64) ([]uint64, error) {
-	randomness[31] = 0 // TODO: Not correct, fixme
+	randomness[31] &= 0x3f
 	return ffi.GenerateWinningPoStSectorChallenge(proofType, minerID, randomness, eligibleSectorCount)
 }