SQL error on taxonomy migrate from d6 to d7

There is nothing abnormal about the taxonomies in either d6 or d7. There are no nested vocabularies.

$drush mi --group=taxonomy

Migration failed with source plugin exception: SQLSTATE[HY000]: General error: 3065 Expression #1 of ORDER BY clause is not in SELECT list, references column [error]
'drupal6_db.th.parent' which is not in SELECT list; this is incompatible with DISTINCT, in class="placeholder">/Library/WebServer/Documents/drupal6_site/includes/database/database.inc:2171

Fixed by removing line 31 "->orderBy('th.parent')" in migrate_d2d/d6/taxonomy.inc

 protected function query() {
    // Note the explode - this supports the (admittedly unusual) case of
    // consolidating multiple vocabularies into one.
    $query = Database::getConnection('default', $this->sourceConnection)
             ->select('term_data', 'td')
             ->fields('td', array('tid', 'name', 'description', 'weight'))
             ->condition('vid', explode(',', $this->sourceVocabulary), 'IN')
         // ->orderBy('th.parent')
             ->distinct();
    // Join to the hierarchy so we can sort on parent, but we'll pull the
    // actual parent values in separately in case there are multiples.
    $query->leftJoin('term_hierarchy', 'th', 'td.tid=th.tid');
    return $query;
  }