diff --git a/code/model/SubsiteDomain.php b/code/model/SubsiteDomain.php
index 8714c04..aabd72a 100644
--- a/code/model/SubsiteDomain.php
+++ b/code/model/SubsiteDomain.php
@@ -2,15 +2,27 @@
 
 class SubsiteDomain extends DataObject {
 
+	/**
+	 *
+	 * @var array
+	 */
 	private static $db = array(
 		"Domain" => "Varchar(255)",
 		"IsPrimary" => "Boolean",
 	);
 
+	/**
+	 *
+	 * @var array
+	 */
 	private static $has_one = array(
  		"Subsite" => "Subsite",
 	);
 
+	/**
+	 *
+	 * @var array
+	 */
 	private static $summary_fields=array(
 		'Domain',
 		'IsPrimary',
@@ -25,13 +37,24 @@ class SubsiteDomain extends DataObject {
 		Subsite::writeHostMap();
 	}
 	
+	/**
+	 * 
+	 * @return \FieldList
+	 */
 	public function getCMSFields() {
-		return new FieldList(
+		$fields = new FieldList(
 			new TextField('Domain', $this->fieldLabel('Domain'), null, 255),
 			new CheckboxField('IsPrimary', $this->fieldLabel('IsPrimary'))
 		);
+		$this->extend('updateCMSFields', $fields);
+		return $fields;
 	}
 
+	/**
+	 * 
+	 * @param bool $includerelations
+	 * @return array
+	 */
 	public function fieldLabels($includerelations = true) {
 		$labels = parent::fieldLabels($includerelations);
 		$labels['Domain'] = _t('SubsiteDomain.DOMAIN', 'Domain');