diff --git a/backend/flaschengeist_events/event_controller.py b/backend/flaschengeist_events/event_controller.py
index 4d60e19..a3853c4 100644
--- a/backend/flaschengeist_events/event_controller.py
+++ b/backend/flaschengeist_events/event_controller.py
@@ -393,7 +393,7 @@ def respond_invitation(invite: Invitation, accepted=True):
         if invite.transferee_id is None:
             assign_job(job, invite.invitee_, 1)
         else:
-            service = filter(lambda s: s.userid == invite.transferee_id, job.services)
+            service = tuple(filter(lambda s: s.userid == invite.transferee_id, job.services))
             if not service:
                 raise Conflict
             unassign_job(job, invite.transferee_, service[0], True)