Error related to call-time pass-by-reference

Switched to a different server (CentOS instead of Ubuntu) and hit this error on module install. I'd consider it minor if it didn't show up on every page load. :)

mailhandler.install:

/**
 * Move human-readable mailbox name into separate field.
 */
function mailhandler_update_6204() {
  $ret = array();
  db_add_field(&$ret, 'mailhandler_mailbox', 'admin_title', array('type' => 'varchar', 'length' => '255', 'description' => 'Human-readable name (email address) of this mailbox.'));

Removing the & from &$ret makes the issue go away.