diff --git a/HACKING.rdoc b/HACKING.rdoc
index 4723352..4173426 100644
--- a/HACKING.rdoc
+++ b/HACKING.rdoc
@@ -42,11 +42,12 @@ environment generated by your request. To try a POST request, start the
 'file_upload.ru' config as above, then use curl (or similar tool) to send a post
 with some file content like so:
 
-> curl -F "test=@README.rdoc" http://localhost:8080/
+> curl -F "file=@README.rdoc" http://localhost:8080/
 
 This command tells curl to send the file as a form parameter, and the reply
 should contain the content of the rack 'params' variable constructed from this
-parameter.
+parameter. In particular, when the parameter is named 'file', the
+'file_upload.ru' sample will return the contents of the file.
 
 
 == Debugging