diff --git a/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php b/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php
index 953acfb..1b62fec 100644
--- a/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php
+++ b/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php
@@ -80,6 +80,12 @@ public function applyToRequest($controller, Request $request) {
 
       $param_name = $param->getName();
 
+      // No need to convert parameters that are already the objects they should
+      // be.
+      if ($param_class->isInstance($request->attributes->get($param_name))) {
+        continue;
+      }
+
       $new_value = $this->convertTo($request->attributes->get($param_name), $param->getClass()->getName());
       $request->attributes->set($param_name, $new_value);
     }