diff --git a/booking.studygroups.inc b/booking.studygroups.inc
index a378eb4..05d5392 100644
--- a/booking.studygroups.inc
+++ b/booking.studygroups.inc
@@ -1061,7 +1061,7 @@ function _booking_studygroups_update_preallocate($group, $group_mapping, &$sessi
  * Process attendee list to allocate attendees to study group sessions based on statistical breakdown of attendees
  * @see booking_studygroups_update_form()
  */
-function _booking_studygroups_update_allocate($iterator, $max_people, $maximums, $group, $group_mapping, $session_count, $working_list, $calculation_messages) {
+function _booking_studygroups_update_allocate($iterator, $max_people, $maximums, $group, $group_mapping, &$session_count, &$working_list, &$calculation_messages) {
 	$starting_session = 0;
 	
 	//reset the iterator to starting position