diff --git a/src/Bundle/ChillActivityBundle/Entity/Activity.php b/src/Bundle/ChillActivityBundle/Entity/Activity.php
index 85abed5e5..693e2af85 100644
--- a/src/Bundle/ChillActivityBundle/Entity/Activity.php
+++ b/src/Bundle/ChillActivityBundle/Entity/Activity.php
@@ -346,8 +346,9 @@ class Activity implements HasCenterInterface, HasScopeInterface, AccompanyingPer
         if (null !== $this->accompanyingPeriod) {
             $personsNotAssociated = [];
 
+            // TODO better semantic with:  return $this->persons->filter(...);
             foreach ($this->persons as $person) {
-                if (!in_array($person, $this->getPersonsAssociated())) {
+                if ($this->accompanyingPeriod->getOpenParticipationContainsPerson($person) === null) {
                     $personsNotAssociated[] = $person;
                 }
             }