diff --git a/guides/source/configuring.md b/guides/source/configuring.md
index c938edd8f7b4675bdf69b10c375b3d026fd9bd58..1ca66f66a5beb722d6bffd63444723ef875d8ba3 100644
--- a/guides/source/configuring.md
+++ b/guides/source/configuring.md
@@ -169,6 +169,8 @@ pipeline is enabled. It is set to `true` by default.
 
 * `config.assets.precompile` allows you to specify additional assets (other than `application.css` and `application.js`) which are to be precompiled when `rake assets:precompile` is run.
 
+* `config.assets.unknown_asset_fallback` allows you to modify the behavior of the asset pipeline when an asset is not in the pipeline with recent verisons of sprockets-rails.
+
 * `config.assets.prefix` defines the prefix where assets are served from. Defaults to `/assets`.
 
 * `config.assets.manifest` defines the full path to be used for the asset precompiler's manifest file. Defaults to a file named `manifest-<random>.json` in the `config.assets.prefix` directory within the public folder.