diff --git a/src/pretix/presale/templates/pretixpresale/fragment_modals.html b/src/pretix/presale/templates/pretixpresale/fragment_modals.html
index d3babc33d2..be95945e6b 100644
--- a/src/pretix/presale/templates/pretixpresale/fragment_modals.html
+++ b/src/pretix/presale/templates/pretixpresale/fragment_modals.html
@@ -48,7 +48,7 @@
 </div>
 <div id="cart-extend-modal" class="modal-wrapper" hidden aria-live="polite" role="dialog"
         aria-labelledby="cart-extend-modal-title" aria-describedby="cart-extend-modal-desc">
-    <dialog class="modal-card" id="cart-extend-modal">
+    <div class="modal-card" id="cart-extend-modal">
         <div class="modal-card-icon">
             <i class="fa fa-clock-o big-icon" aria-hidden="true"></i>
         </div>
@@ -61,7 +61,7 @@
                 <p><button class="btn btn-lg btn-primary">{% trans "Continue" %}</button></p>
             </div>
         </div>
-    </dialog>
+    </div>
 </div>
 {% if request.organizer and request.organizer.settings.cookie_consent %}
     <script type="text/plain" id="cookie-consent-storage-key">cookie-consent-{{ request.organizer.slug }}</script>
diff --git a/src/pretix/static/pretixpresale/js/ui/cart.js b/src/pretix/static/pretixpresale/js/ui/cart.js
index 7d2682ead1..819e819d5c 100644
--- a/src/pretix/static/pretixpresale/js/ui/cart.js
+++ b/src/pretix/static/pretixpresale/js/ui/cart.js
@@ -21,14 +21,14 @@ var cart = {
     },
 
     show_expiry_notification: function () {
-        $("#cart-extend-modal").show();
+        $("#cart-extend-modal").removeAttr("hidden");
         $("#cart-extend-modal button").focus();
         $("body").addClass("has-modal-dialog");
         cart._expiry_notified = true;
     },
 
     hide_expiry_notification: function () {
-        $("#cart-extend-modal").hide();
+        $("#cart-extend-modal").attr("hidden", true);
         $("body").removeClass("has-modal-dialog");
     },
 
@@ -71,7 +71,7 @@ var cart = {
         }
         var can_extend_cart = diff_minutes < 3 && (diff_total_seconds < 0 || cart._deadline < cart._max_extend);
         $("#cart-extend-button").toggle(can_extend_cart);
-        if (can_extend_cart && diff_minutes < 1 && !cart._expiry_notified) cart.show_expiry_notification();
+        if (can_extend_cart && diff_total_seconds < 45 && !cart._expiry_notified) cart.show_expiry_notification();
     },
 
     init: function () {