diff --git a/forms/TabSet.php b/forms/TabSet.php
index bf404993e..dc5ec3b2a 100644
--- a/forms/TabSet.php
+++ b/forms/TabSet.php
@@ -27,6 +27,8 @@
  */
 class TabSet extends CompositeField {
 
+	protected $tabSet;
+
 	/**
 	 * @param string $name Identifier
 	 * @param string $title (Optional) Natural language title of the tabset