diff --git a/packages/react-scripts/template/README.md b/packages/react-scripts/template/README.md
index 157073b74b3..287a0134e95 100644
--- a/packages/react-scripts/template/README.md
+++ b/packages/react-scripts/template/README.md
@@ -944,6 +944,7 @@ To define permanent environment variables, create a file called `.env` in the ro
 ```
 REACT_APP_SECRET_CODE=abcdef
 ```
+>Note: You must create custom environment variables beginning with `REACT_APP_`. Any other variables except `NODE_ENV` will be ignored to avoid [accidentally exposing a private key on the machine that could have the same name](https://github.com/facebookincubator/create-react-app/issues/865#issuecomment-252199527). Changing any environment variables will require you to restart the development server if it is running.
 
 `.env` files **should be** checked into source control (with the exclusion of `.env*.local`).