diff --git a/extern/sector-storage/ffiwrapper/sealer_cgo.go b/extern/sector-storage/ffiwrapper/sealer_cgo.go
index dca8b44b5..36fbacb30 100644
--- a/extern/sector-storage/ffiwrapper/sealer_cgo.go
+++ b/extern/sector-storage/ffiwrapper/sealer_cgo.go
@@ -195,12 +195,16 @@ func (sb *Sealer) AddPiece(ctx context.Context, sector storage.SectorRef, existi
 		return piecePromises[0]()
 	}
 
+	var payloadRoundedBytes abi.PaddedPieceSize
 	pieceCids := make([]abi.PieceInfo, len(piecePromises))
 	for i, promise := range piecePromises {
-		pieceCids[i], err = promise()
+		pinfo, err := promise()
 		if err != nil {
 			return abi.PieceInfo{}, err
 		}
+
+		pieceCids[i] = pinfo
+		payloadRoundedBytes += pinfo.Size
 	}
 
 	pieceCID, err := ffi.GenerateUnsealedCID(sector.ProofType, pieceCids)
@@ -213,6 +217,15 @@ func (sb *Sealer) AddPiece(ctx context.Context, sector storage.SectorRef, existi
 		return abi.PieceInfo{}, err
 	}
 
+	if payloadRoundedBytes < pieceSize.Padded() {
+		paddedCid, err := commpffi.ZeroPadPieceCommitment(pieceCID, payloadRoundedBytes.Unpadded(), pieceSize)
+		if err != nil {
+			return abi.PieceInfo{}, xerrors.Errorf("failed to pad data: %w", err)
+		}
+
+		pieceCID = paddedCid
+	}
+
 	return abi.PieceInfo{
 		Size:     pieceSize.Padded(),
 		PieceCID: pieceCID,
diff --git a/extern/sector-storage/ffiwrapper/sealer_test.go b/extern/sector-storage/ffiwrapper/sealer_test.go
index 2efcfc6a0..39e37f0cc 100644
--- a/extern/sector-storage/ffiwrapper/sealer_test.go
+++ b/extern/sector-storage/ffiwrapper/sealer_test.go
@@ -709,3 +709,46 @@ func BenchmarkAddPiece512M(b *testing.B) {
 		fmt.Println(c)
 	}
 }
+
+func TestAddPiece512MPadded(t *testing.T) {
+	sz := abi.PaddedPieceSize(512 << 20).Unpadded()
+
+	cdir, err := ioutil.TempDir("", "sbtest-c-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	miner := abi.ActorID(123)
+
+	sp := &basicfs.Provider{
+		Root: cdir,
+	}
+	sb, err := New(sp)
+	if err != nil {
+		t.Fatalf("%+v", err)
+	}
+	cleanup := func() {
+		if t.Failed() {
+			fmt.Printf("not removing %s\n", cdir)
+			return
+		}
+		if err := os.RemoveAll(cdir); err != nil {
+			t.Error(err)
+		}
+	}
+	t.Cleanup(cleanup)
+
+	r := rand.New(rand.NewSource(0x7e5))
+
+	c, err := sb.AddPiece(context.TODO(), storage.SectorRef{
+		ID: abi.SectorID{
+			Miner:  miner,
+			Number: 0,
+		},
+		ProofType: abi.RegisteredSealProof_StackedDrg512MiBV1_1,
+	}, nil, sz, io.LimitReader(r, int64(sz/4)))
+	if err != nil {
+		t.Fatalf("add piece failed: %s", err)
+	}
+
+	require.Equal(t, "baga6ea4seaqonenxyku4o7hr5xkzbqsceipf6xgli3on54beqbk6k246sbooobq", c.PieceCID.String())
+}
diff --git a/go.mod b/go.mod
index 86e6da40d..9d5accbf1 100644
--- a/go.mod
+++ b/go.mod
@@ -30,7 +30,7 @@ require (
 	github.com/filecoin-project/go-amt-ipld/v2 v2.1.1-0.20201006184820-924ee87a1349 // indirect
 	github.com/filecoin-project/go-bitfield v0.2.4
 	github.com/filecoin-project/go-cbor-util v0.0.0-20191219014500-08c40a1e63a2
-	github.com/filecoin-project/go-commp-utils v0.1.0
+	github.com/filecoin-project/go-commp-utils v0.1.1-0.20210427191551-70bf140d31c7
 	github.com/filecoin-project/go-crypto v0.0.0-20191218222705-effae4ea9f03
 	github.com/filecoin-project/go-data-transfer v1.4.3
 	github.com/filecoin-project/go-fil-commcid v0.0.0-20201016201715-d41df56b4f6a
diff --git a/go.sum b/go.sum
index 8bcfafdfc..54c5da743 100644
--- a/go.sum
+++ b/go.sum
@@ -260,8 +260,8 @@ github.com/filecoin-project/go-bitfield v0.2.4/go.mod h1:CNl9WG8hgR5mttCnUErjcQj
 github.com/filecoin-project/go-cbor-util v0.0.0-20191219014500-08c40a1e63a2 h1:av5fw6wmm58FYMgJeoB/lK9XXrgdugYiTqkdxjTy9k8=
 github.com/filecoin-project/go-cbor-util v0.0.0-20191219014500-08c40a1e63a2/go.mod h1:pqTiPHobNkOVM5thSRsHYjyQfq7O5QSCMhvuu9JoDlg=
 github.com/filecoin-project/go-commp-utils v0.0.0-20201119054358-b88f7a96a434/go.mod h1:6s95K91mCyHY51RPWECZieD3SGWTqIFLf1mPOes9l5U=
-github.com/filecoin-project/go-commp-utils v0.1.0 h1:PaDxoXYh1TXnnz5kA/xSObpAQwcJSUs4Szb72nuaNdk=
-github.com/filecoin-project/go-commp-utils v0.1.0/go.mod h1:6s95K91mCyHY51RPWECZieD3SGWTqIFLf1mPOes9l5U=
+github.com/filecoin-project/go-commp-utils v0.1.1-0.20210427191551-70bf140d31c7 h1:U9Z+76pHCKBmtdxFV7JFZJj7OVm12I6dEKwtMVbq5p0=
+github.com/filecoin-project/go-commp-utils v0.1.1-0.20210427191551-70bf140d31c7/go.mod h1:6s95K91mCyHY51RPWECZieD3SGWTqIFLf1mPOes9l5U=
 github.com/filecoin-project/go-crypto v0.0.0-20191218222705-effae4ea9f03 h1:2pMXdBnCiXjfCYx/hLqFxccPoqsSveQFxVLvNxy9bus=
 github.com/filecoin-project/go-crypto v0.0.0-20191218222705-effae4ea9f03/go.mod h1:+viYnvGtUTgJRdy6oaeF4MTFKAfatX071MPDPBL11EQ=
 github.com/filecoin-project/go-data-transfer v1.0.1/go.mod h1:UxvfUAY9v3ub0a21BSK9u3pB2aq30Y0KMsG+w9/ysyo=