diff --git a/.eslintrc b/.eslintrc
index db38935..da2592a 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -7,20 +7,26 @@ env:
   browser: true
   node: true
 
-# 0: off, 1: warning, 2: error
 rules:
-  # semicolons are useless
-  semi: [2, "never"]
-
+  indent: [2, 2] # 2 spaces indentation
+  max-len: [2, 80, 4]
   quotes: [2, "double"]
+  semi: [2, "never"]
+  no-multiple-empty-lines: [2, {"max": 1}]
 
-  # 2 spaces indentation
-  indent: [2, 2]
-
-  # trailing coma are cool for diff
+  brace-style: [2, "stroustrup"]
   comma-dangle: [2, "always-multiline"]
-
-  # enforce comma at eol (never before)
   comma-style: [2, "last"]
+  computed-property-spacing: [2, "never"]
+  dot-location: [2, "property"]
+
+  one-var: [2, "never"]
+  no-bitwise: [2]
 
-  valid-jsdoc: 2
+  object-shorthand: [2, "methods"]
+  space-after-keywords: [2, "always"]
+  space-before-blocks: [2, "always"]
+  space-before-function-paren: [2, "never"]
+  space-in-brackets: [2, "never"]
+  space-in-parens: [2, "never"]
+  spaced-line-comment: [2, "always"]
diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa6561c..86b2809 100755
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,8 @@
-# 4.0.0 - Unrelease
+# 4.0.0 - 2015-05-17
 
-- Changed: warning messages are not sent via postcss API (^4.1.0)
+- Changed: warning messages are now sent via postcss messages api (^4.1.0)
+- Added: automatic custom media `--` prefixing
+([#11](https://github.com/postcss/postcss-custom-media/issues/11))
 - Added: `preserve` allows you to preserve custom media query defintions
 - Added: `appendExtensions` allows you (when `preserve` is truthy) to append your extensions as media queries
 
diff --git a/README.md b/README.md
index bbc416a..60a89a3 100755
--- a/README.md
+++ b/README.md
@@ -4,7 +4,9 @@
 
 ## Installation
 
-    $ npm install postcss-custom-media
+```console
+$ npm install postcss-custom-media
+```
 
 ## Usage
 
@@ -45,28 +47,27 @@ Checkout [tests](test) for more examples.
 
 ### Options
 
-#### `extensions` (default: `{}`)
+#### `extensions`
 
-Allows you to pass an object to define the `<media-query-list>` for each `<extension-name>`. These definitions will override any that exist in the CSS.
+(default: `{}`)
 
-#### `preserve` (default: `false`)
+Allows you to pass an object to define the `<media-query-list>` for each
+`<extension-name>`. These definitions will override any that exist in the CSS.
 
-Allows you to preserve custom media query definitions in output.
+#### `preserve`
 
-#### `appendExtensions` (default: `false`)
+(default: `false`)
 
-If `preserve` is set to `true`, allows you to append your extensions at end of your CSS.
+Allows you to preserve custom media query definitions in output.
 
----
+#### `appendExtensions`
 
-## Contributing
+(default: `false`)
 
-Work on a branch, install dev-dependencies, respect coding style & run tests before submitting a bug fix or a feature.
+**This option only works if `preserve` is truthy**.
+Allows you to append your extensions at end of your CSS.
 
-    $ git clone https://github.com/postcss/postcss-custom-media.git
-    $ git checkout -b patch-1
-    $ npm install
-    $ npm test
+---
 
 ## [Changelog](CHANGELOG.md)
 
diff --git a/index.js b/index.js
index 13bc19c..4f7153d 100755
--- a/index.js
+++ b/index.js
@@ -1,18 +1,7 @@
-/**
- * Module dependencies
- */
 var postcss = require("postcss")
 
-/**
- * Constants.
- */
 var EXTENSION_RE = /\(\s*(--[\w-]+)\s*\)/g
 
-/**
- * Expose the plugin.
- */
-module.exports = postcss.plugin("postcss-custom-media", customMedia)
-
 /*
  * read & replace custom media queries by standard media queries
  */
@@ -66,7 +55,11 @@ function customMedia(options) {
           return map[name]
         }
 
-        result.warn("Missing @custom-media definition for '" + name + "'. The entire rule has been removed from the output.", {node: rule})
+        result.warn(
+          "Missing @custom-media definition for '" + name +
+            "'. The entire rule has been removed from the output.",
+          {node: rule}
+        )
         toRemove.push(rule)
       })
     })
@@ -88,6 +81,10 @@ function customMedia(options) {
     }
 
     // remove @custom-media
-    toRemove.forEach(function(rule) { rule.removeSelf() })
+    toRemove.forEach(function(rule) {
+      rule.removeSelf()
+    })
   }
 }
+
+module.exports = postcss.plugin("postcss-custom-media", customMedia)
diff --git a/package.json b/package.json
index 503a9be..8d5ad43 100644
--- a/package.json
+++ b/package.json
@@ -24,7 +24,7 @@
     "postcss": "^4.1.4"
   },
   "devDependencies": {
-    "eslint": "^0.18.0",
+    "eslint": "^0.23.0",
     "tape": "^4.0.0"
   },
   "scripts": {
diff --git a/test/index.js b/test/index.js
index 3e641b7..b73efe2 100755
--- a/test/index.js
+++ b/test/index.js
@@ -5,14 +5,20 @@ var test = require("tape")
 var postcss = require("postcss")
 var plugin = require("..")
 
-function filename(name) { return "test/" + name + ".css" }
-function read(name) { return fs.readFileSync(name, "utf8") }
+function filename(name) {
+  return "test/" + name + ".css"
+}
+function read(name) {
+  return fs.readFileSync(name, "utf8")
+}
 
 function compareFixtures(t, name, msg, opts, postcssOpts) {
   postcssOpts = postcssOpts || {}
   postcssOpts.from = filename("fixtures/" + name)
   opts = opts || {}
-  var result = postcss().use(plugin(opts)).process(read(postcssOpts.from), postcssOpts)
+  var result = postcss()
+    .use(plugin(opts))
+    .process(read(postcssOpts.from), postcssOpts)
   var actual = result.css
   var expected = read(filename("fixtures/" + name + ".expected"))
   fs.writeFile(filename("fixtures/" + name + ".actual"), actual)
@@ -22,35 +28,71 @@ function compareFixtures(t, name, msg, opts, postcssOpts) {
 }
 
 test("@custom-media", function(t) {
-  compareFixtures(t, "transform", "should transform custom media")
-
-  compareFixtures(t, "transform-all", "should replaces all extension names")
-
-  var undefinedRes = compareFixtures(t, "undefined", "should remove undefined @media")
-  t.ok(undefinedRes.warnings()[0].text.match(/Missing @custom-media/), "should send warning to postcss")
-
-  compareFixtures(t, "js-defined", "should transform custom media and override local extensions", {
-    extensions: {
-      "--viewport-max-s": "(max-width: 30em)",
-      "--viewport-min-s": "(min-width: 30.01em)",
-    },
-  })
-
-  compareFixtures(t, "js-defined", "should transform custom media and override local unprefixed extensions", {
-    extensions: {
-      "viewport-max-s": "(max-width: 30em)",
-      "viewport-min-s": "(min-width: 30.01em)",
-    },
-  })
-
-  compareFixtures(t, "preserve", "should preserve custom media", {preserve: true})
-
-  compareFixtures(t, "append", "should append custom media", {
-    extensions: {
-      "--viewport-max-s": "(max-width: 30em)",
-    },
-    appendExtensions: true,
-  })
+  compareFixtures(
+    t,
+    "transform",
+    "should transform custom media"
+  )
+
+  compareFixtures(
+    t,
+    "transform-all",
+    "should replaces all extension names"
+  )
+
+  var undefinedRes = compareFixtures(
+    t,
+    "undefined",
+    "should remove undefined @media"
+  )
+
+  t.ok(
+    undefinedRes.warnings()[0].text.match(/Missing @custom-media/),
+    "should send warning to postcss"
+  )
+
+  compareFixtures(
+    t,
+    "js-defined",
+    "should transform custom media and override local extensions",
+    {
+      extensions: {
+        "--viewport-max-s": "(max-width: 30em)",
+        "--viewport-min-s": "(min-width: 30.01em)",
+      },
+    }
+  )
+
+  compareFixtures(
+    t,
+    "js-defined",
+    "should transform custom media and override local unprefixed extensions",
+    {
+      extensions: {
+        "viewport-max-s": "(max-width: 30em)",
+        "viewport-min-s": "(min-width: 30.01em)",
+      },
+    }
+  )
+
+  compareFixtures(
+    t,
+    "preserve",
+    "should preserve custom media",
+    {preserve: true}
+  )
+
+  compareFixtures(
+    t,
+    "append",
+    "should append custom media",
+    {
+      extensions: {
+        "--viewport-max-s": "(max-width: 30em)",
+      },
+      appendExtensions: true,
+    }
+  )
 
   t.end()
 })