diff --git a/core/modules/rest/src/RequestHandler.php b/core/modules/rest/src/RequestHandler.php
index 54d9d8737f..eebcdb29cc 100644
--- a/core/modules/rest/src/RequestHandler.php
+++ b/core/modules/rest/src/RequestHandler.php
@@ -5,6 +5,7 @@
 use Drupal\Component\Utility\ArgumentsResolver;
 use Drupal\Core\Cache\CacheableResponseInterface;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Symfony\Component\DependencyInjection\ContainerAwareInterface;
@@ -158,10 +159,37 @@ protected function getArgumentResolver(RouteMatchInterface $route_match, $unseri
     // to the raw arguments.
     $raw_route_arguments = $route_match->getRawParameters()->all() + $route->getDefaults();
 
-    $upcasted_route_arguments = $route_match->getParameters()->all();
-    $upcasted_route_arguments['entity'] = $unserialized;
-    $upcasted_route_arguments['data'] = $unserialized;
-    $upcasted_route_arguments['unserialized'] = $unserialized;
+    $route_arguments = $route_match->getParameters()->all();
+    $upcasted_route_arguments = $route_arguments;
+
+    // Just set the values, if they are actually defined, otherwise, the
+    // argument resolver believe 
+    if (isset($unserialized)) {
+      $upcasted_route_arguments['entity'] = $unserialized;
+      $upcasted_route_arguments['data'] = $unserialized;
+      $upcasted_route_arguments['unserialized'] = $unserialized;
+    }
+
+    // In the case of GET the entity is stored in $upcasted_route_arguments in
+    // the $entity_type_id key, not as 'entity', which
+    // \Drupal\rest\Plugin\rest\resource\EntityResource expects as their name.
+    if (empty($upcasted_route_arguments['entity'])) {
+      // Try to find a parameter which is an entity.
+      foreach ($route_arguments as $value) {
+        if ($value instanceof EntityInterface) {
+          $upcasted_route_arguments['entity'] = $value;
+        }
+      }
+    }
+
+    if (empty($upcasted_route_arguments['original_entity'])) {
+      // Try to find a parameter which is an entity.
+      foreach ($route_arguments as $value) {
+        if ($value instanceof EntityInterface) {
+          $upcasted_route_arguments['original_entity'] = $value;
+        }
+      }
+    }
 
     // Parameters which are not defined on the route object, but still are
     // essential for access checking are passed as wildcards to the argument