diff --git a/normalisename.py b/normalisename.py
index a3b8765..228faef 100644
--- a/normalisename.py
+++ b/normalisename.py
@@ -9,8 +9,8 @@ for file in argv[1:]:
            (
                ''.join(ch for ch in file
                        if ch.isalnum()
-                       or ch is ' '
-                       or ch is '.'
+                       or ch is ' '     # whitespaces will be replaced
+                       or ch is '.'     # dots are ok
                        or ch is '_'     # do not ruin previous work
                        or ch is '-')    # dashes are ok
            )