diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 701d624c2..467da348c 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -152,9 +152,10 @@ Test your code and make sure it passes. Our testing harness requires [node.js](h
 and a few modules:
 
 1. [Install node.js](http://nodejs.org/) - 'Install' will download a package for your OS
-2. Go to the directory where you have checked out `iD`
-3. Run `npm install`
-4. Run `npm test` to see whether your tests pass or fail.
+2. Install [PhantomJS](http://phantomjs.org/) - This can be done via `npm install phantomjs` or homebrew
+3. Go to the directory where you have checked out `iD`
+4. Run `npm install`
+5. Run `npm test` to see whether your tests pass or fail.
 
 ## Building / Installing