diff --git a/ffiwrapper/partialfile.go b/ffiwrapper/partialfile.go
index f6c03f1a3..3e8b32288 100644
--- a/ffiwrapper/partialfile.go
+++ b/ffiwrapper/partialfile.go
@@ -285,7 +285,7 @@ func (pf *partialFile) HasAllocated(offset storiface.UnpaddedByteIndex, size abi
 		return false, err
 	}
 
-	u, err := rlepluslazy.Union(have, pieceRun(offset.Padded(), size.Padded()))
+	u, err := rlepluslazy.And(have, pieceRun(offset.Padded(), size.Padded()))
 	if err != nil {
 		return false, err
 	}
diff --git a/ffiwrapper/sealer_test.go b/ffiwrapper/sealer_test.go
index 0b5018d84..f795be159 100644
--- a/ffiwrapper/sealer_test.go
+++ b/ffiwrapper/sealer_test.go
@@ -111,7 +111,7 @@ func (s *seal) unseal(t *testing.T, sb *Sealer, sp *basicfs.Provider, si abi.Sec
 	defer done()
 
 	var b bytes.Buffer
-	err := sb.ReadPiece(context.TODO(), &b, si, 0, 1016)
+	_, err := sb.ReadPiece(context.TODO(), &b, si, 0, 1016)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -130,7 +130,7 @@ func (s *seal) unseal(t *testing.T, sb *Sealer, sp *basicfs.Provider, si abi.Sec
 	}
 	sd()
 
-	err = sb.ReadPiece(context.TODO(), &b, si, 0, 1016)
+	_, err = sb.ReadPiece(context.TODO(), &b, si, 0, 1016)
 	if err == nil {
 		t.Fatal("HOW?!")
 	}
@@ -141,7 +141,7 @@ func (s *seal) unseal(t *testing.T, sb *Sealer, sp *basicfs.Provider, si abi.Sec
 	}
 
 	b.Reset()
-	err = sb.ReadPiece(context.TODO(), &b, si, 0, 1016)
+	_, err = sb.ReadPiece(context.TODO(), &b, si, 0, 1016)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -150,14 +150,17 @@ func (s *seal) unseal(t *testing.T, sb *Sealer, sp *basicfs.Provider, si abi.Sec
 	require.Equal(t, expect, b.Bytes())
 
 	b.Reset()
-	err = sb.ReadPiece(context.TODO(), &b, si, 0, 2032)
+	have, err := sb.ReadPiece(context.TODO(), &b, si, 0, 2032)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	expect = append(expect, bytes.Repeat([]byte{0}, 1016)...)
-	if !bytes.Equal(b.Bytes(), expect) {
-		t.Fatal("read wrong bytes")
+	if have {
+		t.Errorf("didn't expect to read things")
+	}
+
+	if b.Len() != 0 {
+		t.Fatal("read bytes")
 	}
 }
 
diff --git a/sched_test.go b/sched_test.go
index caf7f0b4b..c96f7838c 100644
--- a/sched_test.go
+++ b/sched_test.go
@@ -88,7 +88,7 @@ func (s *schedTestWorker) UnsealPiece(ctx context.Context, id abi.SectorID, inde
 	panic("implement me")
 }
 
-func (s *schedTestWorker) ReadPiece(ctx context.Context, writer io.Writer, id abi.SectorID, index storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize) error {
+func (s *schedTestWorker) ReadPiece(ctx context.Context, writer io.Writer, id abi.SectorID, index storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize) (bool, error) {
 	panic("implement me")
 }
 
diff --git a/testworker_test.go b/testworker_test.go
index bdfff1915..40151a84d 100644
--- a/testworker_test.go
+++ b/testworker_test.go
@@ -53,7 +53,7 @@ func (t *testWorker) UnsealPiece(ctx context.Context, id abi.SectorID, index sto
 	panic("implement me")
 }
 
-func (t *testWorker) ReadPiece(ctx context.Context, writer io.Writer, id abi.SectorID, index storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize) error {
+func (t *testWorker) ReadPiece(ctx context.Context, writer io.Writer, id abi.SectorID, index storiface.UnpaddedByteIndex, size abi.UnpaddedPieceSize) (bool, error) {
 	panic("implement me")
 }