diff --git a/docs/guide/async.rst b/docs/guide/async.rst
index e4ead74b..8d5f27c6 100644
--- a/docs/guide/async.rst
+++ b/docs/guide/async.rst
@@ -78,7 +78,7 @@ callback argument::
         http_client = AsyncHTTPClient()
         def handle_response(response):
             callback(response.body)
-        http_client.fetch(url)
+        http_client.fetch(url, callback=handle_response)
 
 And again with a `.Future` instead of a callback::