diff --git a/src/wp-admin/js/customize-nav-menus.js b/src/wp-admin/js/customize-nav-menus.js
index 1f797b0aa7..a973e3eaf5 100644
--- a/src/wp-admin/js/customize-nav-menus.js
+++ b/src/wp-admin/js/customize-nav-menus.js
@@ -1800,8 +1800,10 @@
 				}
 
 				if ( ! $( 'body' ).hasClass( 'adding-menu-items' ) ) {
+					$( this ).attr( 'aria-expanded', 'true' );
 					api.Menus.availableMenuItemsPanel.open( self );
 				} else {
+					$( this ).attr( 'aria-expanded', 'false' );
 					api.Menus.availableMenuItemsPanel.close();
 					event.stopPropagation();
 				}
diff --git a/src/wp-includes/class-wp-customize-control.php b/src/wp-includes/class-wp-customize-control.php
index 2c2ac8cf60..23a499dfb3 100644
--- a/src/wp-includes/class-wp-customize-control.php
+++ b/src/wp-includes/class-wp-customize-control.php
@@ -1538,7 +1538,7 @@ class WP_Customize_Nav_Menu_Control extends WP_Customize_Control {
 	 */
 	public function content_template() {
 		?>
-		<button type="button" class="button-secondary add-new-menu-item">
+		<button type="button" class="button-secondary add-new-menu-item" aria-expanded="false" aria-controls="available-menu-items">
 			<?php _e( 'Add Items' ); ?>
 		</button>
 		<button type="button" class="not-a-button reorder-toggle">