diff --git a/ffiwrapper/sealer_test.go b/ffiwrapper/sealer_test.go
index c39d0ade0..73eaa2652 100644
--- a/ffiwrapper/sealer_test.go
+++ b/ffiwrapper/sealer_test.go
@@ -16,7 +16,6 @@ import (
 	logging "github.com/ipfs/go-log"
 	"golang.org/x/xerrors"
 
-	ffi "github.com/filecoin-project/filecoin-ffi"
 	paramfetch "github.com/filecoin-project/go-paramfetch"
 	"github.com/filecoin-project/specs-actors/actors/abi"
 
@@ -418,14 +417,3 @@ func TestSealAndVerify2(t *testing.T) {
 
 	post(t, sb, s1, s2)
 }
-
-func TestScribbles(t *testing.T) {
-	rf, w, _ := toReadableFile(bytes.NewReader(bytes.Repeat([]byte{0xff, 0}, 127)), 254)
-	defer w()
-
-	tf, _ := ioutil.TempFile("/tmp/", "scrb-")
-
-	fmt.Println(tf.Name())
-
-	fmt.Println(ffi.WriteWithAlignment(abi.RegisteredProof_StackedDRG2KiBSeal, rf, 254, tf, nil))
-}
diff --git a/mock/mock.go b/mock/mock.go
index 403a1cbf6..53777434c 100644
--- a/mock/mock.go
+++ b/mock/mock.go
@@ -24,6 +24,7 @@ var log = logging.Logger("sbmock")
 
 type SectorMgr struct {
 	sectors      map[abi.SectorID]*sectorState
+	pieces       map[cid.Cid][]byte
 	sectorSize   abi.SectorSize
 	nextSectorID abi.SectorNumber
 	proofType    abi.RegisteredProof
@@ -41,6 +42,7 @@ func NewMockSectorMgr(ssize abi.SectorSize) *SectorMgr {
 
 	return &SectorMgr{
 		sectors:      make(map[abi.SectorID]*sectorState),
+		pieces:       map[cid.Cid][]byte{},
 		sectorSize:   ssize,
 		nextSectorID: 5,
 		proofType:    rt,
@@ -80,13 +82,17 @@ func (mgr *SectorMgr) AddPiece(ctx context.Context, sectorId abi.SectorID, exist
 	ss.lk.Lock()
 	defer ss.lk.Unlock()
 
-	c, err := ffiwrapper.GeneratePieceCIDFromFile(mgr.proofType, r, size)
+	var b bytes.Buffer
+	tr := io.TeeReader(r, &b)
+
+	c, err := ffiwrapper.GeneratePieceCIDFromFile(mgr.proofType, tr, size)
 	if err != nil {
 		return abi.PieceInfo{}, xerrors.Errorf("failed to generate piece cid: %w", err)
 	}
 
 	log.Warn("Generated Piece CID: ", c)
 
+	mgr.pieces[c] = b.Bytes()
 	ss.pieces = append(ss.pieces, c)
 	return abi.PieceInfo{
 		Size:     size.Padded(),
@@ -269,11 +275,11 @@ func generateFakePoSt(sectorInfo []abi.SectorInfo) []abi.PoStProof {
 }
 
 func (mgr *SectorMgr) ReadPiece(ctx context.Context, w io.Writer, sectorID abi.SectorID, offset storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize, randomness abi.SealRandomness, c cid.Cid) error {
-	if len(mgr.sectors[sectorID].pieces) > 1 {
+	if len(mgr.sectors[sectorID].pieces) > 1 || offset != 0 {
 		panic("implme")
 	}
 
-	_, err := io.CopyN(w, bytes.NewReader(mgr.sectors[sectorID].pieces[0].Bytes()[offset:]), int64(size))
+	_, err := io.CopyN(w, bytes.NewReader(mgr.pieces[mgr.sectors[sectorID].pieces[0]]), int64(size))
 	return err
 }