diff --git a/package.json b/package.json
index c014bb3..ae8c42b 100644
--- a/package.json
+++ b/package.json
@@ -3,6 +3,7 @@
   "version": "2.1.3",
   "description": "Modify JavaScript code, generate source map for the modification.",
   "main": "index.js",
+  "module": "esm.mjs",
   "exports": {
     "import": "./esm.mjs",
     "require": "./index.js"