diff --git a/lib/jmap/client.ts b/lib/jmap/client.ts
index 9c3b9b29..c1a0a0d5 100644
--- a/lib/jmap/client.ts
+++ b/lib/jmap/client.ts
@@ -3513,8 +3513,8 @@ export class JMAPClient implements IJMAPClient {
   ): Promise<void> {
     const accountId = targetAccountId || this.getCalendarsAccountId();
 
-    // Strip client-only shared fields before sending to JMAP
-    const { originalId: _oi, originalCalendarIds: _oc, accountId: _ai, accountName: _an, isShared: _is, ...cleanUpdates } = updates as CalendarEvent;
+    // Strip client-only and server-immutable fields before sending to JMAP
+    const { id: _id, uid: _uid, '@type': _typ, created: _cr, updated: _up, sequence: _sq, isOrigin: _io, isDraft: _idr, originalId: _oi, originalCalendarIds: _oc, accountId: _ai, accountName: _an, isShared: _is, ...cleanUpdates } = updates as CalendarEvent;
     cleanRecurrenceRules(cleanUpdates as unknown as Record<string, unknown>);
 
     const setArgs: Record<string, unknown> = {