diff --git a/portal/assets/js/ynh_portal.js b/portal/assets/js/ynh_portal.js
index 84453c6..806f809 100644
--- a/portal/assets/js/ynh_portal.js
+++ b/portal/assets/js/ynh_portal.js
@@ -266,6 +266,7 @@ function init_portal_button_and_overlay()
   portalOverlay.src = "/yunohost/sso/portal.html";
   portalOverlay.setAttribute("id","ynh-overlay");
   portalOverlay.setAttribute("style","visibility: hidden;"); // make sure the overlay is invisible already when loading it
+  portalOverlay.setAttribute("class","ynh-fadeOut"); // set overlay as masked when loading it
   document.body.insertBefore(portalOverlay, null);
 
   // Inject portal button