opts.dst_index = &the_index;
 
        opts.fn = oneway_merge;
-       tree = parse_tree_indirect(current_head->object.sha1);
+       tree = parse_tree_indirect(current_head->object.oid.hash);
        if (!tree)
                die(_("failed to unpack HEAD tree object"));
        parse_tree(tree);
        if (!transaction ||
            ref_transaction_update(transaction, "HEAD", sha1,
                                   current_head
-                                  ? current_head->object.sha1 : null_sha1,
+                                  ? current_head->object.oid.hash : null_sha1,
                                   0, sb.buf, &err) ||
            ref_transaction_commit(transaction, &err)) {
                rollback_index_files();
                cfg = init_copy_notes_for_rewrite("amend");
                if (cfg) {
                        /* we are amending, so current_head is not NULL */
-                       copy_note_for_rewrite(cfg, current_head->object.sha1, sha1);
+                       copy_note_for_rewrite(cfg, current_head->object.oid.hash, sha1);
                        finish_copy_notes_for_rewrite(cfg, "Notes added by 'git commit --amend'");
                }
-               run_rewrite_hook(current_head->object.sha1, sha1);
+               run_rewrite_hook(current_head->object.oid.hash, sha1);
        }
        if (!quiet)
                print_summary(prefix, sha1, !current_head);