diff --git a/src/ReflectionClass.php b/src/ReflectionClass.php
index a069f16..bd57035 100644
--- a/src/ReflectionClass.php
+++ b/src/ReflectionClass.php
@@ -115,7 +115,7 @@ public static function getRefId(mixed &$reference, ?\SplObjectStorage $keepAlive
         }
 
         // we save this so the ref ids cannot be reused while serializing/deserializing
-        $keepAlive?->attach($ref);
+        $keepAlive?->offsetSet($ref);
 
         return $ref->getId();
     }
@@ -148,4 +148,4 @@ public static function getRawProperties(object $object, array $properties, ?stri
 
         return $data;
     }
-}
\ No newline at end of file
+}
diff --git a/src/SerializationHandler.php b/src/SerializationHandler.php
index 602fe1c..de43d9d 100644
--- a/src/SerializationHandler.php
+++ b/src/SerializationHandler.php
@@ -125,7 +125,7 @@ private function handleObject(object $data): object
         if ($data instanceof stdClass) {
             // handle stdClass
             $obj = $this->handleStdClass($data);
-            $this->priority->attach($obj);
+            $this->priority->offsetSet($obj);
             return $obj;
         }
 
@@ -158,7 +158,7 @@ private function handleObject(object $data): object
         $box->data[1] = $this->getObjectVars($data, $info);
 
         // Add to priority
-        $this->priority->attach($box);
+        $this->priority->offsetSet($box);
 
         return $box;
     }
@@ -289,4 +289,4 @@ private function &getCachedInfo(AbstractInfo $info): array
         $this->info[$key] ??= $info->__serialize();
         return $this->info[$key];
     }
-}
\ No newline at end of file
+}