diff --git a/qutebrowser/config/configtypes.py b/qutebrowser/config/configtypes.py
index 5d6acc0db..46af59069 100644
--- a/qutebrowser/config/configtypes.py
+++ b/qutebrowser/config/configtypes.py
@@ -122,6 +122,7 @@ class BaseType:
     """
 
     special = False
+    valid_values = None
 
     def __init__(self, none_ok=False):
         self.none_ok = none_ok