diff --git a/storage/wdpost_run.go b/storage/wdpost_run.go
index 64f5690298a..93598c988e7 100644
--- a/storage/wdpost_run.go
+++ b/storage/wdpost_run.go
@@ -473,6 +473,19 @@ func (s *WindowPoStScheduler) runPost(ctx context.Context, di dline.Info, ts *ty
 		posts[i].ChainCommitRand = commRand
 	}
 
+	// Compute randomness after generating proofs so as to reduce the impact
+	// of chain reorgs (which change randomness)
+	commEpoch := di.Open
+	commRand, err := s.api.ChainGetRandomnessFromTickets(ctx, ts.Key(), crypto.DomainSeparationTag_PoStChainCommit, commEpoch, nil)
+	if err != nil {
+		return nil, xerrors.Errorf("failed to get chain randomness for windowPost (ts=%d; deadline=%d): %w", ts.Height(), di, err)
+	}
+
+	for i := range posts {
+		posts[i].ChainCommitEpoch = commEpoch
+		posts[i].ChainCommitRand = commRand
+	}
+
 	return posts, nil
 }
 
diff --git a/storage/wdpost_run_test.go b/storage/wdpost_run_test.go
index 47972fe7fd7..7b76bff62f8 100644
--- a/storage/wdpost_run_test.go
+++ b/storage/wdpost_run_test.go
@@ -19,6 +19,8 @@ import (
 	"github.com/filecoin-project/specs-actors/actors/builtin/miner"
 	"github.com/filecoin-project/specs-actors/actors/runtime/proof"
 
+	"github.com/filecoin-project/go-state-types/dline"
+
 	"github.com/filecoin-project/go-state-types/abi"
 	"github.com/filecoin-project/go-state-types/crypto"
 	tutils "github.com/filecoin-project/specs-actors/support/testing"
@@ -154,7 +156,7 @@ func TestWDPostDoPost(t *testing.T) {
 		worker:       workerAct,
 	}
 
-	di := &miner.DeadlineInfo{}
+	di := &dline.Info{}
 	ts := mockTipSet(t)
 	scheduler.doPost(ctx, di, ts)
 
@@ -218,7 +220,7 @@ func (m *mockStorageMinerAPI) StateSectorPartition(ctx context.Context, maddr ad
 	panic("implement me")
 }
 
-func (m *mockStorageMinerAPI) StateMinerProvingDeadline(ctx context.Context, address address.Address, key types.TipSetKey) (*miner.DeadlineInfo, error) {
+func (m *mockStorageMinerAPI) StateMinerProvingDeadline(ctx context.Context, address address.Address, key types.TipSetKey) (*dline.Info, error) {
 	panic("implement me")
 }