diff --git a/extern/sector-storage/manager.go b/extern/sector-storage/manager.go
index 300958e39..86a739c19 100644
--- a/extern/sector-storage/manager.go
+++ b/extern/sector-storage/manager.go
@@ -217,16 +217,11 @@ func (m *Manager) ReadPiece(ctx context.Context, sink io.Writer, sector abi.Sect
 		return xerrors.Errorf("read piece: checking for already existing unsealed sector: %w", err)
 	}
 
+	var readOk bool
 	var selector WorkerSelector
 	if len(best) == 0 { // new
 		selector = newAllocSelector(m.index, stores.FTUnsealed, stores.PathSealing)
 	} else { // append to existing
-		selector = newExistingSelector(m.index, sector, stores.FTUnsealed, false)
-	}
-
-	var readOk bool
-
-	if len(best) > 0 {
 		// There is unsealed sector, see if we can read from it
 
 		selector = newExistingSelector(m.index, sector, stores.FTUnsealed, false)
@@ -257,6 +252,10 @@ func (m *Manager) ReadPiece(ctx context.Context, sink io.Writer, sector abi.Sect
 		return nil
 	}
 
+	if unsealed == cid.Undef {
+		return xerrors.Errorf("cannot unseal piece (sector: %d, offset: %d size: %d) - unsealed cid is undefined", sector, offset, size)
+	}
+
 	err = m.sched.Schedule(ctx, sector, sealtasks.TTUnseal, selector, unsealFetch, func(ctx context.Context, w Worker) error {
 		return w.UnsealPiece(ctx, sector, offset, size, ticket, unsealed)
 	})