diff --git a/plugins/libcalendaring/libcalendaring.js b/plugins/libcalendaring/libcalendaring.js
index 73d1c1ec..5dcc3d46 100644
--- a/plugins/libcalendaring/libcalendaring.js
+++ b/plugins/libcalendaring/libcalendaring.js
@@ -23,12 +23,16 @@
 function rcube_libcalendaring(settings)
 {
     // member vars
-    this.settings = settings;
+    this.settings = settings || {};
     this.alarm_ids = [];
     this.alarm_dialog = null;
     this.snooze_popup = null;
     this.dismiss_link = null;
 
+    // abort if env isn't set
+    if (!settings || !settings.date_format)
+      return;
+
     // private vars
     var me = this;
     var gmt_offset = (new Date().getTimezoneOffset() / -60) - (settings.timezone || 0) - (settings.dst || 0);