diff --git a/qa/qa_utils.py b/qa/qa_utils.py
index 463240c0aa05995e12e11624950d3ef289401cb7..9384a6c4ba491daa6988abeb253e759a7fdb51f8 100644
--- a/qa/qa_utils.py
+++ b/qa/qa_utils.py
@@ -267,6 +267,8 @@ def DefineHook(name):
 
   Usage: prefix function with @qa_utils.DefineHook(...)
 
+  This based on PEP 318, "Decorators for Functions and Methods".
+
   """
   def wrapper(fn):
     def new_f(*args, **kwargs):