diff --git a/letsencrypt/client/client.py b/letsencrypt/client/client.py
index dd484cc31..763178d19 100644
--- a/letsencrypt/client/client.py
+++ b/letsencrypt/client/client.py
@@ -343,7 +343,7 @@ def init_key(key_size):
         key_pem = crypto_util.make_key(key_size)
     except ValueError as err:
         logging.fatal(str(err))
-        logging.info("Note: The default RSA key size is %d bits." % CONFIG.RSA_KEY_SIZE)
+        logging.info("Note: The default RSA key size is %d bits.", CONFIG.RSA_KEY_SIZE)
         sys.exit(1)
 
     # Save file