diff --git a/core/modules/rest/src/RequestHandler.php b/core/modules/rest/src/RequestHandler.php
index 0ddfdd7..0cb2ef9 100644
--- a/core/modules/rest/src/RequestHandler.php
+++ b/core/modules/rest/src/RequestHandler.php
@@ -63,7 +63,13 @@ public function handle(RouteMatchInterface $route_match, Request $request, Route
         $definition = $resource->getPluginDefinition();
         $class = $definition['serialization_class'];
         try {
-          $unserialized = $serializer->deserialize($received, $class, $format, array('request_method' => $method));
+          if ($class) {
+            $unserialized = $serializer->deserialize($received, $class, $format, array('request_method' => $method));
+          }
+          // Avoid denormalization because we need to instantiate a class.
+          else {
+            $unserialized = $serializer->decode($received, $format, array('request_method' => $method));
+          }
         }
         catch (UnexpectedValueException $e) {
           $error['error'] = $e->getMessage();