diff --git a/classes/cascadecohortsync.php b/classes/cascadecohortsync.php
index d10eed7..63792ee 100644
--- a/classes/cascadecohortsync.php
+++ b/classes/cascadecohortsync.php
@@ -118,7 +118,7 @@ class cascadecohortsync {
                     if(!in_array($this->studyplanid ,$plans)){
                         // if not, add it to the reference
                         $this->debug->write("Adding this plan to the list");
-                        $plans[] = $this->studyplanid;
+                        $plans[] = (int)($this->studyplanid);
                         $enrol->update_instance($instance,(object)["customtext4"=>json_encode($plans)]);
                     }
 
@@ -139,7 +139,7 @@ class cascadecohortsync {
                         // in the customtext4 field in json format
                         $this->debug->write("Instance ({$instanceid} created. Updateing instance with studyplan id");
                         $instance = $DB->get_record('enrol', array('id' => $instanceid));
-                        $enrol->update_instance($instance,(object)["customtext4"=>json_encode([$this->studyplanid])]);
+                        $enrol->update_instance($instance,(object)["customtext4"=>json_encode([(int)($this->studyplanid)])]);
                         
                         $this->debug->write("Synchronize the enrolment");
                         // Successfully added a valid new instance, so now instantiate it.