diff --git a/index.js b/index.js
index e16398f..6103658 100644
--- a/index.js
+++ b/index.js
@@ -7,7 +7,7 @@
  * @typedef {import('unist').Node} Node
  */
 
-var hast2mdast = require('hast-util-to-mdast')
+import hast2mdast from 'hast-util-to-mdast'
 
 /**
  * Attacher.
@@ -19,7 +19,7 @@ var hast2mdast = require('hast-util-to-mdast')
  * @param destination Optional unified processor.
  * @param options Options passed to `hast-util-to-mdast`.
  */
-module.exports =
+const rehypeRemark =
   /**
    * @type {import('unified').Plugin<[Options?]|[Processor, Options?]>}
    */
@@ -49,6 +49,8 @@ module.exports =
     }
   )
 
+export default rehypeRemark
+
 /**
  * Bridge-mode.
  * Runs the destination with the new mdast tree.
@@ -62,10 +64,10 @@ function bridge(destination, options) {
   function transformer(node, file, next) {
     destination.run(hast2mdast(node, options), file, done)
     /** @type {RunCallback} */
-    function done(err) {
+    function done(error) {
       // @ts-expect-error: `unified` should accept 1 arg for next.
       // See: <https://github.com/unifiedjs/unified/pull/141#issuecomment-871239574>
-      next(err)
+      next(error)
     }
   }
 }
diff --git a/package.json b/package.json
index f965fb4..0957f6c 100644
--- a/package.json
+++ b/package.json
@@ -24,17 +24,18 @@
   "contributors": [
     "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
   ],
+  "sideEffects": false,
+  "type": "module",
+  "main": "index.js",
+  "files": [
+    "index.js"
+  ],
   "dependencies": {
     "@types/hast": "^2.0.0",
     "@types/mdast": "^3.0.0",
     "@types/unist": "^2.0.0",
     "hast-util-to-mdast": "^7.0.0"
   },
-  "types": "index.d.ts",
-  "files": [
-    "index.js",
-    "index.d.ts"
-  ],
   "devDependencies": {
     "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
@@ -49,7 +50,7 @@
     "type-coverage": "^2.0.0",
     "typescript": "^4.0.0",
     "unified": "^9.0.0",
-    "xo": "^0.36.0"
+    "xo": "^0.38.0"
   },
   "scripts": {
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
@@ -68,10 +69,10 @@
   },
   "xo": {
     "prettier": true,
-    "esnext": false,
-    "ignores": [
-      "rehype-remark.js"
-    ]
+    "rules": {
+      "no-var": "off",
+      "prefer-arrow-callback": "off"
+    }
   },
   "remarkConfig": {
     "plugins": [
diff --git a/test.js b/test.js
index 1f6937d..1a47c4b 100644
--- a/test.js
+++ b/test.js
@@ -1,5 +1,3 @@
-'use strict'
-
 /**
  * @typedef {import('./index.js').Options} Options
  * @typedef {import('./index.js').Handle} Handle
@@ -7,12 +5,12 @@
  * @typedef {import('hast').Text} Text
  */
 
-var test = require('tape')
-var unified = require('unified')
-var parse = require('rehype-parse')
-var markdown = require('remark-stringify')
-var html = require('rehype-stringify')
-var rehype2remark = require('.')
+import test from 'tape'
+import unified from 'unified'
+import parse from 'rehype-parse'
+import markdown from 'remark-stringify'
+import html from 'rehype-stringify'
+import rehype2remark from './index.js'
 
 test('rehype2remark()', function (t) {
   t.equal(
@@ -74,7 +72,7 @@ test('handlers option', function (t) {
        * @type {Handle}
        * @param {Element & {tagName: 'div'}} node
        */
-      div: function (h, node) {
+      div(h, node) {
         /** @type {Text} */
         // @ts-expect-error: there’s one text child.
         const child = node.children[0]