diff --git a/storage/filesystem/object.go b/storage/filesystem/object.go
index 21667fa5a..a5f694964 100644
--- a/storage/filesystem/object.go
+++ b/storage/filesystem/object.go
@@ -545,6 +545,9 @@ func (s *ObjectStorage) HashesWithPrefix(prefix []byte) ([]plumbing.Hash, error)
 
 	// TODO: This could be faster with some idxfile changes,
 	// or diving into the packfile.
+	if err := s.requireIndex(); err != nil {
+		return nil, err
+	}
 	for _, index := range s.index {
 		ei, err := index.Entries()
 		if err != nil {