diff --git a/package.json b/package.json
index 6b999f7..6886f1b 100644
--- a/package.json
+++ b/package.json
@@ -28,7 +28,7 @@
     "openpgp": "^2.3.0"
   },
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.0.2",
     "co-mocha": "^1.1.2",
     "grunt": "^1.0.1",
     "grunt-contrib-jshint": "^1.0.0",