diff --git a/app/mailers/group_mailer.rb b/app/mailers/group_mailer.rb
index b60bb7422..e9d24e415 100644
--- a/app/mailers/group_mailer.rb
+++ b/app/mailers/group_mailer.rb
@@ -19,8 +19,9 @@ def event_created_confirmation event
     )
   end
 
-  def event_joined_confirmation event
-    user = event.user
+  def event_joined_confirmation event_id, user_id
+    event = Outing.find(event_id)
+    user = User.find(user_id)
 
     IcalService.attach_ical(group: event, for_user: user, to: self)
 
diff --git a/app/observers/join_request_observer.rb b/app/observers/join_request_observer.rb
index af998438e..17bb37c5c 100644
--- a/app/observers/join_request_observer.rb
+++ b/app/observers/join_request_observer.rb
@@ -32,8 +32,9 @@ def action(verb, record)
   end
 
   def mailer(record)
-    if record.joinable.respond_to?(:outing?) && record.joinable.outing?
-      GroupMailer.event_joined_confirmation(record.joinable).deliver_later
-    end
+    return unless record.user
+    return unless record.joinable.respond_to?(:outing?) && record.joinable.outing?
+
+    GroupMailer.event_joined_confirmation(record.joinable_id, record.user_id).deliver_later
   end
 end
diff --git a/spec/mailers/group_mailer_spec.rb b/spec/mailers/group_mailer_spec.rb
index 3e594cffa..80cb19127 100644
--- a/spec/mailers/group_mailer_spec.rb
+++ b/spec/mailers/group_mailer_spec.rb
@@ -1,15 +1,15 @@
 require 'rails_helper'
 
 describe GroupMailer, type: :mailer do
-  let(:user) { create :public_user }
-  let(:outing) { create :outing, user: user }
+  let(:participant) { create :public_user, first_name: 'Alice' }
+  let(:organizer) { create :public_user, first_name: 'Bob' }
+  let(:outing) { create :outing, user: organizer }
 
   describe ".event_joined_confirmation" do
-    let(:user) { create :public_user }
-    let(:mail) { GroupMailer.event_joined_confirmation(outing) }
+    let(:mail) { GroupMailer.event_joined_confirmation(outing.id, participant.id) }
     let(:json_variables) { JSON.parse(mail['X-MJ-Vars'].value) }
 
-    it { expect(json_variables['first_name']).to eq(user.first_name) }
+    it { expect(json_variables['first_name']).to eq(participant.first_name) }
     it { expect(json_variables).to have_key("outing") }
     it { expect(json_variables['outing']['name']).to eq(outing.title) }
     it { expect(json_variables['outing']['calendar_url']).to match("agenda") }