diff --git a/utils.h b/utils.h
index f242c39..e374b5b 100644
--- a/utils.h
+++ b/utils.h
@@ -473,7 +473,7 @@
 // extents are read from the file at |path|. |out_data_size| is the size of
 // |out_data|. Returns false if the number of bytes to read given in
 // |extents| does not equal |out_data_size|.
-bool ReadExtents(const std::string& path, std::vector<Extent>* extents,
+bool ReadExtents(const std::string& path, const std::vector<Extent>& extents,
                  chromeos::Blob* out_data, ssize_t out_data_size,
                  size_t block_size);