diff --git a/package.json b/package.json
index 6bea11b..71b4222 100644
--- a/package.json
+++ b/package.json
@@ -27,7 +27,7 @@
     "mandrill-api": "^1.0.45"
   },
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.0.0",
     "coveralls": "^2.11.12",
     "istanbul": "^0.4.4",
     "mocha": "^3.0.2",