@Override
  public int indexOf(@CheckForNull Object target) {
    int index = delegateCollection().indexOf(target);

    // TODO(kevinb): reconsider if it's really worth making feeble attempts at
    // sanity for inconsistent comparators.

    // The equals() check is needed when the comparator isn't compatible with
    // equals().
    return (index >= 0 && get(index).equals(target)) ? index : -1;