diff --git a/resources/CheckboxHack.d.ts b/resources/CheckboxHack.d.ts
index d2fa76e7e..23f774bd4 100644
--- a/resources/CheckboxHack.d.ts
+++ b/resources/CheckboxHack.d.ts
@@ -1,6 +1,6 @@
 interface CheckboxHack {
-	updateAriaExpanded(checkbox: HTMLInputElement): void;
-	bindUpdateAriaExpandedOnInput(checkbox: HTMLInputElement): CheckboxHackListeners;
+	updateAriaExpanded(checkbox: HTMLInputElement, button: HTMLElement): void;
+	bindUpdateAriaExpandedOnInput(checkbox: HTMLInputElement, button: HTMLElement): CheckboxHackListeners;
 	bindToggleOnClick(checkbox: HTMLInputElement, button: HTMLElement): CheckboxHackListeners;
 	bindDismissOnClickOutside(window: Window, checkbox: HTMLInputElement, button: HTMLElement, target: Node): CheckboxHackListeners;
 	bindDismissOnFocusLoss(window: Window, checkbox: HTMLInputElement, button: HTMLElement, target: Node): CheckboxHackListeners;
diff --git a/resources/skins.vector.js/skin.js b/resources/skins.vector.js/skin.js
index 0da980abe..b19ff3411 100644
--- a/resources/skins.vector.js/skin.js
+++ b/resources/skins.vector.js/skin.js
@@ -46,9 +46,9 @@ function initSidebar( document ) {
 	var button = document.getElementById( 'mw-sidebar-button' );
 	if ( checkbox instanceof HTMLInputElement && button ) {
 		checkboxHack.bindToggleOnClick( checkbox, button );
-		checkboxHack.bindUpdateAriaExpandedOnInput( checkbox );
+		checkboxHack.bindUpdateAriaExpandedOnInput( checkbox, button );
 
-		checkboxHack.updateAriaExpanded( checkbox );
+		checkboxHack.updateAriaExpanded( checkbox, button );
 	}
 }