header.version = htons(default_version);
        header.options = htons(flags | options);
        header.entry_count = htonl(writer.selected_nr);
-       memcpy(header.checksum, writer.pack_checksum, 20);
+       hashcpy(header.checksum, writer.pack_checksum);
 
        sha1write(f, &header, sizeof(header));
        dump_bitmap(f, writer.commits);