diff --git a/main/inc/lib/course.lib.php b/main/inc/lib/course.lib.php
index e2a0c84def..ce16fe1e07 100644
--- a/main/inc/lib/course.lib.php
+++ b/main/inc/lib/course.lib.php
@@ -1537,7 +1537,7 @@ class CourseManager {
         $result = Database::query($sql);
         
         while ($group_data = Database::fetch_array($result)) {
-            $group_data[] = GroupManager::number_of_students($group_data['id'], $course_id);
+            $group_data['userNb'] = GroupManager::number_of_students($group_data['id'], $course_id);
             $group_list[$group_data['id']] = $group_data;
         }
         return $group_list;