diff --git a/src/Proxy/ProxyGenerator.php b/src/Proxy/ProxyGenerator.php
index 8019d418f..ec6fb1004 100644
--- a/src/Proxy/ProxyGenerator.php
+++ b/src/Proxy/ProxyGenerator.php
@@ -201,7 +201,7 @@ public function __setInitialized($initialized): void
      * {@inheritDoc}
      * @internal generated method: use only when explicitly handling proxy specific loading logic
      */
-    public function __setInitializer(\Closure $initializer = null): void
+    public function __setInitializer(?\Closure $initializer = null): void
     {
         $this->__initializer__ = $initializer;
     }
@@ -219,7 +219,7 @@ public function __getInitializer(): ?\Closure
      * {@inheritDoc}
      * @internal generated method: use only when explicitly handling proxy specific loading logic
      */
-    public function __setCloner(\Closure $cloner = null): void
+    public function __setCloner(?\Closure $cloner = null): void
     {
         $this->__cloner__ = $cloner;
     }