diff --git a/forms/TabSet.php b/forms/TabSet.php
index defcfbe52..03ff06689 100644
--- a/forms/TabSet.php
+++ b/forms/TabSet.php
@@ -129,7 +129,7 @@ class TabSet extends CompositeField {
 	/**
 	 * Add a new child field to the end of the set.
 	 */
-	public function push($field) {
+	public function push(FormField $field) {
 		parent::push($field);
 		$field->setTabSet($this);
 	}
@@ -155,4 +155,4 @@ class TabSet extends CompositeField {
 	public function removeByName( $tabName, $dataFieldOnly = false ) {
 		parent::removeByName( $tabName, $dataFieldOnly );
 	}
-}
\ No newline at end of file
+}