diff --git a/Modules/Test/classes/class.ilTestParticipantsGUI.php b/Modules/Test/classes/class.ilTestParticipantsGUI.php
index b010b2e6cd94..3239c6f86d91 100644
--- a/Modules/Test/classes/class.ilTestParticipantsGUI.php
+++ b/Modules/Test/classes/class.ilTestParticipantsGUI.php
@@ -244,43 +244,31 @@ public function showCmd(): void
 
     protected function applyFilterCriteria(array $in_rows): array
     {
-        $selected_pax = ilSession::get('form_tst_participants_' . $this->getTestObj()->getRefId());
+        $selected_pax = ilSession::get('form_tst_participants_' . $this->getTestObj()->getRefId() . '_selection');
 
-        if ($selected_pax === null || !isset($selected_pax['selection'])) {
+        if ($selected_pax === null) {
             return $in_rows;
         }
 
-        $sess_filter = $selected_pax['selection'];
-        $sess_filter = str_replace('"', '', $sess_filter);
-        $sess_filter = explode(':', $sess_filter);
-        $filter = substr($sess_filter[2], 0, strlen($sess_filter[2]) - 1);
+        $filter = unserialize($selected_pax, ['allowed_classes' => false]);
 
-        if ($filter == 'all' || $filter == false) {
-            return $in_rows; #unchanged - no filter.
+        if (!is_string($filter) || $filter === 'all') {
+            return $in_rows;
         }
 
-        $with_result = array();
-        $without_result = array();
+        $with_result = [];
+        $without_result = [];
         foreach ($in_rows as $row) {
             $result = $this->db->query(
                 'SELECT count(solution_id) count
 				FROM tst_solutions
 				WHERE active_fi = ' . $this->db->quote($row['active_id'])
             );
-            $count = $this->db->fetchAssoc($result);
-            $count = $count['count'];
 
-            if ($count == 0) {
-                $without_result[] = $row;
-            } else {
-                $with_result[] = $row;
-            }
+            $this->db->fetchAssoc($result)['count'] === 0 ? $without_result[] = $row : $with_result[] = $row;
         }
 
-        if ($filter == 'withSolutions') {
-            return $with_result;
-        }
-        return $without_result;
+        return $filter === 'withSolutions' ? $with_result : $without_result;
     }
 
     protected function initToolbarControls(ilTestParticipantList $participant_list): void