diff --git a/core/model/ComponentSet.php b/core/model/ComponentSet.php
index a8e0278f5bf..41266788088 100755
--- a/core/model/ComponentSet.php
+++ b/core/model/ComponentSet.php
@@ -89,9 +89,8 @@ function add($item, $extraFields = null) {
 		}
 		
 		if(is_object($item)) {
-			// TODO Should this allow subclasses?
-      		if($item->class != $this->childClass) {
-      			user_error("ComponentSet::add() Tried to add an '{$item->class}' object, but '{$this->childClass}' expected", E_USER_ERROR);
+      		if(!is_a($item, $this->childClass)) {
+      			user_error("ComponentSet::add() Tried to add an '{$item->class}' object, but a '{$this->childClass}' object expected", E_USER_ERROR);
       		}
 		} else {
 			$id = $item;
@@ -196,8 +195,8 @@ function setByIDList($idList) {
 	 */
 	function remove($item) {
 		if(is_object($item)) {
-			if($item->class != $this->childClass && !is_subclass_of($item, $this->childClass)) {
-				user_error("ComponentSet::remove() Tried to remove an '{$item->class}' object, but '{$this->childClass}' expected", E_USER_ERROR);
+			if(!is_a($item, $this->childClass)) {
+				user_error("ComponentSet::remove() Tried to remove an '{$item->class}' object, but a '{$this->childClass}' object expected", E_USER_ERROR);
 			}
 		} else {
 			$item = DataObject::get_by_id($this->childClass, $item);