diff --git a/package.json b/package.json
index e309d3b..19644fb 100644
--- a/package.json
+++ b/package.json
@@ -35,7 +35,7 @@
   "homepage": "https://github.com/the-grid/html-flatten",
   "devDependencies": {
     "brfs": "^1.4.3",
-    "chai": "^3.5.0",
+    "chai": "^4.0.0",
     "coffee-script": "^1.10.0",
     "coffeeify": "^2.0.1",
     "coffeelint": "^1.15.7",