diff --git a/es/index.js b/es/index.js
index 16a08f3ae8f30b8184f5e6decefdc1f66b0f1b64..aa97d18a201b2121ab5f865c60d5de9f5913eae6 100644
--- a/es/index.js
+++ b/es/index.js
@@ -1,6 +1,6 @@
 import { parse } from '@bbob/parser';
-import { iterate, match } from './utils';
-import { C1, C2 } from './errors';
+import { iterate, match } from './utils.js';
+import { C1, C2 } from './errors.js';
 export function createTree(tree, options) {
     const extendedTree = tree;
     extendedTree.messages = [