diff --git a/SoObjects/Appointments/SOGoAppointmentFolder.m b/SoObjects/Appointments/SOGoAppointmentFolder.m
index 915fd4aa5..f0d310bd7 100644
--- a/SoObjects/Appointments/SOGoAppointmentFolder.m
+++ b/SoObjects/Appointments/SOGoAppointmentFolder.m
@@ -3157,6 +3157,8 @@ firstInstanceCalendarDateRange: (NGCalendarDateRange *) fir
                                     inContainer: self];
   [object setIsNew: YES];
   content = [NSMutableString stringWithString: @"BEGIN:VCALENDAR\n"];
+  [content appendFormat: @"PRODID:-//Inverse inc./SOGo %@//EN\n", SOGoVersion];
+
   if (timezone)
     [content appendFormat: @"%@\n",  [timezone versitString]];
   [content appendFormat: @"%@\nEND:VCALENDAR", [event versitString]];