diff --git a/package.json b/package.json
index e789b0b..d7f3ced 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,7 @@
   "author": "ForbesLindesay",
   "license": "MIT",
   "dependencies": {
-    "acorn": "^3.1.0",
+    "acorn": "^4.0.1",
     "acorn-globals": "^3.0.0"
   },
   "devDependencies": {