src/EventSubscriber/ResourceResponseSubscriber.php | 5 ++++-
 tests/src/Functional/ResourceTestBase.php          | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/EventSubscriber/ResourceResponseSubscriber.php b/src/EventSubscriber/ResourceResponseSubscriber.php
index 7d96e71..bfc12ce 100644
--- a/src/EventSubscriber/ResourceResponseSubscriber.php
+++ b/src/EventSubscriber/ResourceResponseSubscriber.php
@@ -8,6 +8,8 @@ use Drupal\Core\Cache\CacheableResponseInterface;
 use Drupal\Core\Render\RenderContext;
 use Drupal\Core\Render\RendererInterface;
 use Drupal\jsonapi\Normalizer\Value\JsonApiDocumentTopLevelNormalizerValue;
+use Drupal\jsonapi\Normalizer\Value\RelationshipNormalizerValue;
+use Drupal\jsonapi\Normalizer\Value\ValueExtractorInterface;
 use Drupal\jsonapi\ResourceResponse;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Component\HttpFoundation\Request;
@@ -142,7 +144,8 @@ class ResourceResponseSubscriber implements EventSubscriberInterface {
     }
   }
 
-  protected static function toArray(JsonApiDocumentTopLevelNormalizerValue $jsonapi_doc_object) {
+  protected static function toArray(ValueExtractorInterface $jsonapi_doc_object) {
+    assert($jsonapi_doc_object instanceof JsonApiDocumentTopLevelNormalizerValue || $jsonapi_doc_object instanceof RelationshipNormalizerValue);
     $jsonapi_doc_array = $jsonapi_doc_object->rasterizeValue();
     $included = array_filter($jsonapi_doc_object->rasterizeIncludes());
     if (!empty($included)) {
diff --git a/tests/src/Functional/ResourceTestBase.php b/tests/src/Functional/ResourceTestBase.php
index b1e0d1c..807dcd0 100644
--- a/tests/src/Functional/ResourceTestBase.php
+++ b/tests/src/Functional/ResourceTestBase.php
@@ -326,7 +326,7 @@ abstract class ResourceTestBase extends BrowserTestBase {
       // Pass a Request object to the normalizer; this will be considered the
       // "current request" for generating the "self" link.
       'request' => Request::create($url->toString(TRUE)->getGeneratedUrl()),
-    ]);
+    ])->rasterizeValue();
   }
 
   /**