diff --git a/lib/index.js b/lib/index.js
index 311ca71..b35a47e 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -1,12 +1,13 @@
 'use strict'
 
 var acorn = require('acorn')
+require('acorn-es7-plugin')(acorn)
 var MagicString = require('magic-string')
 var walk = require('estree-walker').walk
 
 function optimizeJs (jsString, opts) {
   opts = opts || {}
-  var ast = acorn.parse(jsString)
+  var ast = acorn.parse(jsString, { ecmaVersion: 8, allowReserved: true, plugins: { asyncawait: true } })
   var magicString = new MagicString(jsString)
 
   walk(ast, {
diff --git a/package.json b/package.json
index 2690cfc..4541292 100644
--- a/package.json
+++ b/package.json
@@ -22,6 +22,7 @@
   "license": "Apache-2.0",
   "dependencies": {
     "acorn": "^3.3.0",
+    "acorn-es7-plugin": "^1.1.7",
     "concat-stream": "^1.5.1",
     "estree-walker": "^0.3.0",
     "magic-string": "^0.16.0",
diff --git a/test/cases/async-function/input.js b/test/cases/async-function/input.js
new file mode 100644
index 0000000..f1aef22
--- /dev/null
+++ b/test/cases/async-function/input.js
@@ -0,0 +1,3 @@
+!function (){}()
+async function runIt(fun){ fun() }
+runIt(function (){})
\ No newline at end of file
diff --git a/test/cases/async-function/output.js b/test/cases/async-function/output.js
new file mode 100644
index 0000000..9176b34
--- /dev/null
+++ b/test/cases/async-function/output.js
@@ -0,0 +1,3 @@
+!(function (){})()
+async function runIt(fun){ fun() }
+runIt((function (){}))
\ No newline at end of file