diff --git a/normalisename.py b/normalisename.py
index 5743fe9..a3b8765 100644
--- a/normalisename.py
+++ b/normalisename.py
@@ -11,6 +11,7 @@ for file in argv[1:]:
                        if ch.isalnum()
                        or ch is ' '
                        or ch is '.'
+                       or ch is '_'     # do not ruin previous work
                        or ch is '-')    # dashes are ok
            )
            .replace(' ', '_'))