diff --git a/src/SerializationHandler.php b/src/SerializationHandler.php
index d5b0c67..602fe1c 100644
--- a/src/SerializationHandler.php
+++ b/src/SerializationHandler.php
@@ -163,8 +163,6 @@ private function handleObject(object $data): object
         return $box;
     }
 
-    private SplObjectStorage $keep;
-
     private function &handleArray(array &$data, bool $skipRefId = false): array
     {
         if ($skipRefId) {