diff --git a/lib/endpoints/class-wp-rest-terms-controller.php b/lib/endpoints/class-wp-rest-terms-controller.php
index <HASH>..<HASH> 100644
--- a/lib/endpoints/class-wp-rest-terms-controller.php
+++ b/lib/endpoints/class-wp-rest-terms-controller.php
@@ -640,6 +640,7 @@ class WP_REST_Terms_Controller extends WP_REST_Controller {
 			$query_params['parent'] = array(
 				'description'        => 'Limit result set to terms assigned to a specific parent term.',
 				'type'               => 'integer',
+				'sanitize_callback'  => 'absint',
 			);
 		}
 		return $query_params;
Sanitize with `absint` so we get the proper argument type