read_cache_preload(&s.pathspec);
        refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, &s.pathspec, NULL, NULL);
 
-       fd = hold_locked_index(&index_lock, 0);
+       if (use_optional_locks())
+               fd = hold_locked_index(&index_lock, 0);
+       else
+               fd = -1;
 
        s.is_initial = get_oid(s.reference, &oid) ? 1 : 0;
        if (!s.is_initial)
        diff_setup_done(&rev.diffopt);
 
        head = resolve_ref_unsafe("HEAD", 0, NULL, NULL);
+       if (!head)
+               die_errno(_("unable to resolve HEAD after creating commit"));
        if (!strcmp(head, "HEAD"))
                head = _("detached HEAD");
        else