diff --git a/src/Normalizer/ResourceObjectNormalizer.php b/src/Normalizer/ResourceObjectNormalizer.php
index 0785a78..12f93b3 100644
--- a/src/Normalizer/ResourceObjectNormalizer.php
+++ b/src/Normalizer/ResourceObjectNormalizer.php
@@ -75,7 +75,7 @@ class ResourceObjectNormalizer extends NormalizerBase {
     }
     /* @var Value\FieldNormalizerValueInterface[] $normalizer_values */
     $normalizer_values = [];
-    foreach ($object->getFields() as $field_name => $field) {
+    foreach ($this->getFields($object) as $field_name => $field) {
       $normalized_field = $this->serializeField($field, $context, $format);
       assert($normalized_field instanceof FieldNormalizerValueInterface);
 
@@ -91,6 +91,19 @@ class ResourceObjectNormalizer extends NormalizerBase {
     return new ResourceObjectNormalizerValue($normalizer_values, $object, $link_context);
   }
 
+  /**
+   * Extracts a resource object's fields.
+   *
+   * @param \Drupal\jsonapi\JsonApiResource\ResourceObject $object
+   *   The resource object from which to extract fields.
+   *
+   * @return \Drupal\Core\Field\FieldItemListInterface[]|mixed
+   *   The extracted fields.
+   */
+  protected function getFields(ResourceObject $object) {
+    return $object->getFields();
+  }
+
   /**
    * Gets the field names for the given entity.
    *