diff --git a/src/components/WindowTopMenuButton.js b/src/components/WindowTopMenuButton.js
index 1ff393ae74..5a3ca886eb 100644
--- a/src/components/WindowTopMenuButton.js
+++ b/src/components/WindowTopMenuButton.js
@@ -48,6 +48,7 @@ export class WindowTopMenuButton extends Component {
     return (
       <>
         <MiradorMenuButton
+          aria-expanded={!!anchorEl}
           aria-haspopup="true"
           aria-label={t('windowMenu')}
           aria-owns={anchorEl ? `window-menu_${windowId}` : undefined}