diff --git a/ChangeLog b/ChangeLog
index 8748a06d8..c3b88205b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2011-10-03  Ludovic Marcotte  <lmarcotte@inverse.ca>
+
+	* SoObjects/Appointments/SOGoAppointmentObject.m (-PUTAction:)
+	We compare sequence numbers to make sure we correctly accept
+	invitation replies for the "right" objects
+
 2011-09-30  Wolfgang Sourdeau  <wsourdeau@inverse.ca>
 
 	* OpenChange/MAPIStoreMailMessage.m (-getMessageData:inMemCtx:):
diff --git a/Documentation/SOGo Native Microsoft Outlook Configuration.odt b/Documentation/SOGo Native Microsoft Outlook Configuration.odt
index 9a47058bf..5c4d86093 100644
Binary files a/Documentation/SOGo Native Microsoft Outlook Configuration.odt and b/Documentation/SOGo Native Microsoft Outlook Configuration.odt differ
diff --git a/SoObjects/Appointments/SOGoAppointmentObject.m b/SoObjects/Appointments/SOGoAppointmentObject.m
index e4e8e9452..c288b3d22 100644
--- a/SoObjects/Appointments/SOGoAppointmentObject.m
+++ b/SoObjects/Appointments/SOGoAppointmentObject.m
@@ -1833,6 +1833,13 @@
 	      
 	      attendee = [newEvent userAsAttendee: [SOGoUser userWithLogin: owner]];
 	      
+	      // We first check of the sequences are alright. We don't accept attendees
+	      // accepting "old" invitations. If that's the case, we return a 403
+              if ([[newEvent sequence] intValue] < [[oldEvent sequence] intValue])
+		return [NSException exceptionWithHTTPStatus:403
+				    reason: @"sequences don't match"];
+	      
+
 	      delegate = nil;
 	      delegateEmail = [attendee delegatedTo];