diff --git a/user_mgmt/users.py b/user_mgmt/users.py
index 6d8685d..2006bef 100644
--- a/user_mgmt/users.py
+++ b/user_mgmt/users.py
@@ -102,7 +102,7 @@ def _username_valid(username):
         ascii_username = unidecode.unidecode(username).replace("'", '').replace(' ', '').lower()
         if ascii_username != username:
             return False
-        if not re.fullmatch('[\w\-\._]+', username):
+        if not re.fullmatch(r'[\w\-\._]+', username):
             return False
         if len(username) < 5:
             return False