diff --git a/src/pretix/static/pretixpresale/js/ui/main.js b/src/pretix/static/pretixpresale/js/ui/main.js
index f757c0481..72204ba62 100644
--- a/src/pretix/static/pretixpresale/js/ui/main.js
+++ b/src/pretix/static/pretixpresale/js/ui/main.js
@@ -232,6 +232,16 @@ function setup_basics(el) {
     });
 }
 
+function setup_week_calendar() {
+    // Week calendar
+    // On mobile, auto-collapse all days except today, if we have more than 15 events in total
+    if ($(window).width() < 992 && $(".week-calendar .event").length > 15) {
+        $(".week-calendar .weekday:not(.today)").each(function () {
+            $(this).prop("open", false);
+        });
+    }
+}
+
 $(function () {
     "use strict";
 
@@ -528,12 +538,11 @@ $(function () {
         }
     });
 
-    // Week calendar
-    // On mobile, auto-collapse all days except today, if we have more than 15 events in total
-    if ($(window).width() < 992 && $(".week-calendar .event").length > 15) {
-        $(".week-calendar .weekday:not(.today)").each(function () {
-            $(this).prop("open", false);
-        });
+    // For a very weird reason, window width is 0 on an initial load of the widget
+    if ($(window).width() > 0) {
+        setup_week_calendar()
+    } else {
+        $(window).on('resize', setup_week_calendar)
     }
 
     // Day calendar