diff --git a/lib/emails/EventAttendeeMail.ts b/lib/emails/EventAttendeeMail.ts
index b8bef1ba..55f231f9 100644
--- a/lib/emails/EventAttendeeMail.ts
+++ b/lib/emails/EventAttendeeMail.ts
@@ -1,6 +1,13 @@
 import dayjs, {Dayjs} from "dayjs";
 import EventMail from "./EventMail";
 
+import utc from 'dayjs/plugin/utc';
+import timezone from 'dayjs/plugin/timezone';
+import localizedFormat from 'dayjs/plugin/localizedFormat';
+dayjs.extend(utc);
+dayjs.extend(timezone);
+dayjs.extend(localizedFormat);
+
 export default class EventAttendeeMail extends EventMail {
   /**
    * Returns the email text as HTML representation.
diff --git a/lib/emails/EventOrganizerMail.ts b/lib/emails/EventOrganizerMail.ts
index 86c23e42..6d3060b6 100644
--- a/lib/emails/EventOrganizerMail.ts
+++ b/lib/emails/EventOrganizerMail.ts
@@ -2,6 +2,15 @@ import {createEvent} from "ics";
 import dayjs, {Dayjs} from "dayjs";
 import EventMail from "./EventMail";
 
+import utc from 'dayjs/plugin/utc';
+import timezone from 'dayjs/plugin/timezone';
+import toArray from 'dayjs/plugin/toArray';
+import localizedFormat from 'dayjs/plugin/localizedFormat';
+dayjs.extend(utc);
+dayjs.extend(timezone);
+dayjs.extend(toArray);
+dayjs.extend(localizedFormat);
+
 export default class EventOrganizerMail extends EventMail {
   /**
    * Returns the instance's event as an iCal event in string representation.