diff --git a/.babelrc b/.babelrc
deleted file mode 100644
index 22e308d..0000000
--- a/.babelrc
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-	presets: ["es2015"]
-}
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index 57ddb3a..d3a4e10 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,4 @@
 node_modules/
-lib/
 *.sw[po]
 yarn.lock
 package-lock.json
diff --git a/README.md b/README.md
index 9ade18a..309651e 100644
--- a/README.md
+++ b/README.md
@@ -105,7 +105,4 @@ In most cases, you won't need this at all.
 
 ## Development
 
-This module is written in ES6, and uses Babel for compilation. What this means in practice:
-
-* The source code lives in the `src/` directory.
-* After changing this code, make sure to run `npm run build` to compile it.
+This module is written in ES6 and uses ESM.
diff --git a/index.js b/index.js
index 651c499..b0df682 100644
--- a/index.js
+++ b/index.js
@@ -1 +1,4 @@
-module.exports = require("./lib").default;
+/* eslint-disable-next-line no-underscore-dangle */
+const _require = require('esm')(module);
+
+module.exports = _require('./src/index').default;
diff --git a/package.json b/package.json
index fa95452..791dd7c 100644
--- a/package.json
+++ b/package.json
@@ -1,11 +1,10 @@
 {
   "name": "express-ws",
-  "version": "4.0.0",
+  "version": "5.0.0",
   "description": "WebSocket endpoints for Express applications",
-  "main": "index.js",
+  "main": "index",
+  "module": "src/index",
   "scripts": {
-    "prepublish": "npm run build",
-    "build": "babel src/ -d lib/",
     "lint": "eslint src/"
   },
   "author": "Henning Morud <henning@morud.org>",
@@ -15,10 +14,12 @@
     "Andrew Phillips <theasp@gmail.com>",
     "Nicholas Schell <nschell@gmail.com>",
     "Max Truxa <dev@maxtruxa.com>",
-    "Kræn Hansen <mail@kraenhansen.dk>"
+    "Kræn Hansen <mail@kraenhansen.dk>",
+    "Alexis Tyler <xo@wvvw.me>"
   ],
   "license": "BSD-2-Clause",
   "dependencies": {
+    "esm": "^3.0.84",
     "ws": "^6.0.0"
   },
   "peerDependencies": {
@@ -44,8 +45,6 @@
   },
   "homepage": "https://github.com/HenningM/express-ws",
   "devDependencies": {
-    "babel-cli": "^6.26.0",
-    "babel-preset-es2015": "^6.5.0",
     "eslint": "^4.19.0",
     "eslint-config-airbnb": "^14.1.0",
     "eslint-plugin-import": "^2.12.0",
diff --git a/src/index.js b/src/index.js
index e3d3114..dab6c66 100644
--- a/src/index.js
+++ b/src/index.js
@@ -60,7 +60,7 @@ export default function expressWs(app, httpServer, options = {}) {
     dummyResponse.writeHead = function writeHead(statusCode) {
       if (statusCode > 200) {
         /* Something in the middleware chain signalled an error. */
-        dummyResponse._header = '';
+        dummyResponse._header = ''; // eslint-disable-line no-underscore-dangle
         socket.close();
       }
     };