diff --git a/miner/miner.go b/miner/miner.go
index d24850d9f..4075c8cc6 100644
--- a/miner/miner.go
+++ b/miner/miner.go
@@ -409,7 +409,7 @@ func (m *Miner) mineOne(ctx context.Context, base *MiningBase) (*types.BlockMsg,
 		return nil, xerrors.Errorf("failed to marshal miner address: %w", err)
 	}
 
-	rand, err := store.DrawRandomness(rbase.Data, crypto.DomainSeparationTag_WinningPoStChallengeSeed, base.TipSet.Height()+base.NullRounds+1, buf.Bytes())
+	rand, err := store.DrawRandomness(rbase.Data, crypto.DomainSeparationTag_WinningPoStChallengeSeed, round, buf.Bytes())
 	if err != nil {
 		return nil, xerrors.Errorf("failed to get randomness for winning post: %w", err)
 	}