diff --git a/normalisename.py b/normalisename.py
index b055aa2..4b7e563 100644
--- a/normalisename.py
+++ b/normalisename.py
@@ -9,7 +9,7 @@ from os.path import join as joinpath
 # dots are ok
 # do not ruin previous work
 # dashes are ok
-whitelist = [' ', '.', '_', '-']
+whitelist = (' ', '.', '_', '-')
 
 for path in argv[1:]:
     dir = dirname(path)