diff --git a/package.json b/package.json
index 7c1b972..53eb734 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,7 @@
   },
   "devDependencies": {
     "browserify": "^14.1.0",
-    "chai": "^3.5.0",
+    "chai": "^4.0.0",
     "istanbul": "^0.4.5",
     "memdown": "^1.0.0",
     "mocha": "^3.2.0",