diff --git a/includes/sortable-argument-ui.xml b/includes/sortable-argument-ui.xml
index 8781c922..aa9f3c5f 100644
--- a/includes/sortable-argument-ui.xml
+++ b/includes/sortable-argument-ui.xml
@@ -17,4 +17,7 @@
 	<property name="sender" type="jQuery">
 		<desc>The sortable that the item comes from if moving from one sortable to another.</desc>
 	</property>
+	<property name="placeholder" type="jQuery">
+		<desc>The jQuery object representing the element being used as a placeholder.</desc>
+	</property>
 </argument>
\ No newline at end of file