diff --git a/calendar/classes/local/event/mappers/create_update_form_mapper.php b/calendar/classes/local/event/mappers/create_update_form_mapper.php
index e4ef1e80c77..2a9b0cb9990 100644
--- a/calendar/classes/local/event/mappers/create_update_form_mapper.php
+++ b/calendar/classes/local/event/mappers/create_update_form_mapper.php
@@ -109,6 +109,9 @@ class create_update_form_mapper implements create_update_form_mapper_interface {
             } else {
                 $properties->courseid = $data->courseid;
             }
+            if (empty($properties->groupid)) {
+                $properties->groupid = 0;
+            }
         }
 
         // Decode the form fields back into valid event property.