diff --git a/src/JsonApiResource/ResourceObject.php b/src/JsonApiResource/ResourceObject.php
index 2bad23b..08a9be2 100644
--- a/src/JsonApiResource/ResourceObject.php
+++ b/src/JsonApiResource/ResourceObject.php
@@ -180,10 +180,12 @@ final class ResourceObject implements CacheableDependencyInterface, ResourceIden
     $enabled_public_fields = [];
     $fields = $entity->toArray();
     // Filter the array based on the field names.
-    $enabled_field_names = array_filter(
-      array_keys($fields),
-      [$this->resourceType, 'isFieldEnabled']
-    );
+    $enabled_field_names = array_filter(array_keys($fields), function ($internal_field_name) {
+      // Config entities have "fields" which aren't known to the resource type,
+      // these fields should not be excluded because they cannot be enabled or
+      // disabled.
+      return !$this->resourceType->hasField($internal_field_name) || $this->resourceType->isFieldEnabled($internal_field_name);
+    });
     // Return a sub-array of $output containing the keys in $enabled_fields.
     $input = array_intersect_key($fields, array_flip($enabled_field_names));
     /* @var \Drupal\Core\Config\Entity\ConfigEntityInterface $entity */