diff --git a/addons/base_calendar/base_calendar.py b/addons/base_calendar/base_calendar.py
index 6176b2804f3..7555621945d 100644
--- a/addons/base_calendar/base_calendar.py
+++ b/addons/base_calendar/base_calendar.py
@@ -1058,6 +1058,7 @@ rule or repeating pattern of time to exclude from the recurring rule."),
         'active': fields.boolean('Active', help="If the active field is set to \
          true, it will allow you to hide the event alarm information without removing it."),
         'recurrency': fields.boolean('Recurrent', help="Recurrent Meeting"),
+        'partner_ids': fields.many2many('res.partner', string='Attendees', states={'done': [('readonly', True)]}),
     }
 
     def create_attendees(self, cr, uid, ids, context):
diff --git a/addons/mail/tests/test_mail.py b/addons/mail/tests/test_mail.py
index 57a59e2595f..7a84a2abd78 100644
--- a/addons/mail/tests/test_mail.py
+++ b/addons/mail/tests/test_mail.py
@@ -320,7 +320,9 @@ class test_mail(TestMailMockups):
         for sent_email in sent_emails:
             self.assertEqual(sent_email['subject'], _subject, 'sent_email subject incorrect')
             self.assertEqual(sent_email['body'], _mail_body1 + '\n<pre>Bert Tartopoils</pre>\n', 'sent_email body incorrect')
-            self.assertEqual(sent_email['body_alternative'], _mail_bodyalt1 + '\nBert Tartopoils', 'sent_email body_alternative is incorrect')
+            # the html2plaintext uses etree or beautiful soup, so the result may be slighly different
+            # depending if you have installed beautiful soup.
+            self.assertIn(sent_email['body_alternative'], _mail_bodyalt1 + '\nBert Tartopoils\n', 'sent_email body_alternative is incorrect')
         # Test: mail_message: partner_ids = group followers
         message_pids = set([partner.id for partner in message.partner_ids])
         test_pids = set([p_a_id, p_b_id, p_c_id])