core/modules/rest/src/RequestHandler.php | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/core/modules/rest/src/RequestHandler.php b/core/modules/rest/src/RequestHandler.php
index ca8318e..aea0509 100644
--- a/core/modules/rest/src/RequestHandler.php
+++ b/core/modules/rest/src/RequestHandler.php
@@ -162,35 +162,30 @@ protected function getArgumentResolver(RouteMatchInterface $route_match, $unseri
     $route_arguments = $route_match->getParameters()->all();
     $upcasted_route_arguments = $route_arguments;
 
-    // \Drupal\rest\Plugin\ResourceInterface plugins historically receive the
-    // unserialized request body as the N+1th method argument, where N is the
-    // number of route parameters specified on the accompanying route. To be
-    // able to use the argument resolver, which is not based on position but on
-    // name and typehint, specify commonly used names here. 0 or 1 of these will
-    // be used.
-    if (isset($unserialized)) {
+    // For request methods that have request bodies, ResourceInterface plugin
+    // methods historically receive the unserialized request body as the N+1th
+    // method argument, where N is the number of route parameters specified on
+    // the accompanying route. To be able to use the argument resolver, which is
+    // not based on position but on name and typehint, specify commonly used
+    // names here. Similarly, those methods receive the original stored object
+    // as the first method argument.
+    if (in_array($request->getMethod(), ['PATCH', 'POST'], TRUE)) {
       $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 $entity_type_id key, not as 'entity', which
-    // \Drupal\rest\Plugin\rest\resource\EntityResource::get() expects as their name.
-    if (!in_array($request->getMethod(), ['PATCH', 'POST'], TRUE) && 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;
+          $upcasted_route_arguments['original_entity'] = $value;
         }
       }
     }
-
-    if (in_array($request->getMethod(), ['PATCH', 'POST'], TRUE) && empty($upcasted_route_arguments['original_entity'])) {
+    else {
       // Try to find a parameter which is an entity.
       foreach ($route_arguments as $value) {
         if ($value instanceof EntityInterface) {
-          $upcasted_route_arguments['original_entity'] = $value;
+          $upcasted_route_arguments['entity'] = $value;
         }
       }
     }