diff --git a/utils.go b/utils.go
index b235a8a83..21d6b76bf 100644
--- a/utils.go
+++ b/utils.go
@@ -50,7 +50,7 @@ func fillersFromRem(toFill uint64) ([]uint64, error) {
 func (m *Sealing) fastPledgeCommitment(size uint64, parts uint64) (commP [sectorbuilder.CommLen]byte, err error) {
 	parts = 1 << bits.Len64(parts) // round down to nearest power of 2
 
-	piece := sectorbuilder.UserBytesForSectorSize(size / parts)
+	piece := sectorbuilder.UserBytesForSectorSize((size + size / 127) / parts)
 	out := make([]sectorbuilder.PublicPieceInfo, parts)
 	var lk sync.Mutex
 
diff --git a/utils_test.go b/utils_test.go
index 14d512a52..9f9ca3880 100644
--- a/utils_test.go
+++ b/utils_test.go
@@ -49,7 +49,7 @@ func TestFastPledge(t *testing.T) {
 	sz := uint64(16 << 20)
 
 	s := Sealing{sb: sbmock.NewMockSectorBuilder(0, sz)}
-	if _, err := s.fastPledgeCommitment(sz, 5); err != nil {
+	if _, err := s.fastPledgeCommitment(sectorbuilder.UserBytesForSectorSize(sz), 5); err != nil {
 		t.Fatalf("%+v", err)
 	}
 }