diff --git a/package.json b/package.json
index fb35221af..8eaeff7af 100644
--- a/package.json
+++ b/package.json
@@ -81,6 +81,6 @@
     "test": "mocha-webpack --webpack-config source/webpack.test.config.js --require source-map-support/register --require test/helpers/browser.js \"test/**/*.test.js\"",
     "test-watch": "mocha-webpack --webpack-config source/webpack.test.config.js --require source-map-support/register --require test/helpers/browser.js \"test/**/*.test.js\" --watch",
     "test-meca": "mocha-webpack --webpack-config source/webpack.test.config.js --require source-map-support/register --require test/helpers/browser.js test/mecanisms.test.js",
-    "heroku-postbuild": "webpack -p --config source/webpack.config.js --progress"
+    "heroku-postbuild": "npm install --dev && webpack -p --config source/webpack.config.js --progress"
   }
 }