--- a/webdav3/urn.py
+++ b/webdav3/urn.py
@@ -8,7 +8,7 @@
     def __init__(self, path, directory=False):
 
         self._path = quote(path)
-        expressions = "/\.+/", "/+"
+        expressions = (r"/\.+/", "/+")
         for expression in expressions:
             self._path = sub(expression, Urn.separate, self._path)