diff --git a/src/services/Lists.php b/src/services/Lists.php
index 9f39edd..5257011 100644
--- a/src/services/Lists.php
+++ b/src/services/Lists.php
@@ -443,7 +443,7 @@ private function _getListsIdsToPurge($limit = null, $offset = null): array
 
         $guestIds = $query->column();
 
-        return array_merge($userIds, $guestIds);
+        return array_values(array_unique(array_merge($userIds, $guestIds)));
     }
 
 }