diff --git a/src/exercises/async_fn.md b/src/exercises/async_fn.md
index 285de55..5c2256b 100644
--- a/src/exercises/async_fn.md
+++ b/src/exercises/async_fn.md
@@ -1,6 +1,6 @@
 # Async `to_string`
 
-Make this compile and pass tests:
+Define the `AsyncToString` trait to make this compile and pass tests (don't edit existing code):
 
 ```rust,ignore,mdbook-runnable
 # extern crate futures;