system_update_180 error - upgrading from 4.5 to 4.7 - Can't DROP 'vid'.

Downloaded drupal-cvs today. installed and ran update.php on a 4.5 site. Updates 111-179 were fine.
Update 180 reports
Can't DROP 'vid'. Check that column/key exists query: ALTER TABLE node DROP INDEX vid in

The server is running Apache 2.0.51, php 4.3.11, and mysql 3.23.58

function system_update_180() {
  $ret = array();

  if ($GLOBALS['db_type'] == 'mysql') {
    $ret[] = update_sql("ALTER TABLE {node} DROP PRIMARY KEY");
    $ret[] = update_sql("ALTER TABLE {node} ADD PRIMARY KEY (nid, vid)");
    $ret[] = update_sql("ALTER TABLE {node} DROP INDEX vid");
    $ret[] = update_sql("ALTER TABLE {node} ADD UNIQUE (vid)");
    $ret[] = update_sql("ALTER TABLE {node} ADD INDEX (nid)");

    $ret[] = update_sql("ALTER TABLE {node_counter} CHANGE nid nid INT(10) NOT NULL DEFAULT '0'");
  }
  else { // pgsql
    // Insert queries here.
  }

  return $ret;
}

is there a recommended workaround?