diff --git a/diceware/random_sources.py b/diceware/random_sources.py
index 5d08a591e4fb567d070f55213d889ad58f5c4f77..27a718359a6d824c806e0a422aa9e9ec0e96eec2 100644
--- a/diceware/random_sources.py
+++ b/diceware/random_sources.py
@@ -74,7 +74,7 @@ from random import SystemRandom
 
 input_func = input
 if sys.version[0] < "3":
-    input_func = raw_input
+    input_func = raw_input  # NOQA: F821  # defined in python 2 only.
 
 
 class SystemRandomSource(object):