diff --git a/src/wp-includes/rest-api.php b/src/wp-includes/rest-api.php
index 5ec557547c..97af03bf0c 100644
--- a/src/wp-includes/rest-api.php
+++ b/src/wp-includes/rest-api.php
@@ -102,14 +102,14 @@ function register_rest_route( $namespace, $route, $args = array(), $override = f
  * @param array  $args {
  *     Optional. An array of arguments used to handle the registered field.
  *
- *     @type string|array|null $get_callback    Optional. The callback function used to retrieve the field
- *                                              value. Default is 'null', the field will not be returned in
- *                                              the response.
- *     @type string|array|null $update_callback Optional. The callback function used to set and update the
- *                                              field value. Default is 'null', the value cannot be set or
- *                                              updated.
- *     @type string|array|null $schema          Optional. The callback function used to create the schema for
- *                                              this field. Default is 'null', no schema entry will be returned.
+ *     @type callable|null $get_callback    Optional. The callback function used to retrieve the field value. Default is
+ *                                          'null', the field will not be returned in the response. The function will
+ *                                          be passed the prepared object data.
+ *     @type callable|null $update_callback Optional. The callback function used to set and update the field value. Default
+ *                                          is 'null', the value cannot be set or updated. The function will be passed
+ *                                          the model object, like WP_Post.
+ *     @type array|null $schema             Optional. The callback function used to create the schema for this field.
+ *                                          Default is 'null', no schema entry will be returned.
  * }
  */
 function register_rest_field( $object_type, $attribute, $args = array() ) {
diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
index cd976f3357..631eb482bd 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
@@ -372,11 +372,11 @@ abstract class WP_REST_Controller {
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param array           $object  Data object.
-	 * @param WP_REST_Request $request Full details about the request.
+	 * @param array           $prepared Prepared response.
+	 * @param WP_REST_Request $request  Full details about the request.
 	 * @return array Modified data object with additional fields.
 	 */
-	protected function add_additional_fields_to_object( $object, $request ) {
+	protected function add_additional_fields_to_object( $prepared, $request ) {
 
 		$additional_fields = $this->get_additional_fields();
 
@@ -392,10 +392,10 @@ abstract class WP_REST_Controller {
 				continue;
 			}
 
-			$object[ $field_name ] = call_user_func( $field_options['get_callback'], $object, $field_name, $request, $this->get_object_type() );
+			$prepared[ $field_name ] = call_user_func( $field_options['get_callback'], $prepared, $field_name, $request, $this->get_object_type() );
 		}
 
-		return $object;
+		return $prepared;
 	}
 
 	/**
@@ -403,7 +403,7 @@ abstract class WP_REST_Controller {
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param array           $object  Data Object.
+	 * @param object          $object  Data model like WP_Term or WP_Post.
 	 * @param WP_REST_Request $request Full details about the request.
 	 * @return bool|WP_Error True on success, WP_Error object if a field cannot be updated.
 	 */