diff --git a/README.md b/README.md
index 10beab0895..d7db0605ef 100644
--- a/README.md
+++ b/README.md
@@ -311,7 +311,7 @@ There are no guidelines yet. Do what feels natural. Submit a bug, join a discuss
 ### Building documentation
 
 1. Clone [docs repository](https://github.com/phoenixframework/docs) into `../docs`. Relative to your `phoenix` directory.
-2. Run `mix run release_docs.exs` in `phoenix` directory.
+2. Run `MIX_ENV=docs mix run release_docs.exs` in `phoenix` directory.
 3. Change directory to `../docs`.
 4. Commit and push docs.