diff --git a/README.md b/README.md
index 95d5f4b..b758a28 100644
--- a/README.md
+++ b/README.md
@@ -220,12 +220,13 @@ Looking for more plugins? Check out the [contrib/plugins](https://git.mills.io/p
 
 ## Hooks
 
-There are two special plugin names that are executed every time the build
-happens:
+There are two special plugin names that are executed every time the build happens:
 
 - `prehook`  -- executed before the build
 - `posthook` -- executed after the build
 
+You must have `prehook` for `posthook` to work correctly, and `posthook` will only run if a file has been modified.
+
 You can use these to customize the build before and after. For example you can use the `posthook` to minify CSS or Javascript files.
 
 `.zs/posthook`: