diff --git a/qutebrowser/config/conftypes.py b/qutebrowser/config/conftypes.py
index a2ebada50..0b49e0a73 100644
--- a/qutebrowser/config/conftypes.py
+++ b/qutebrowser/config/conftypes.py
@@ -122,7 +122,7 @@ class BaseType:
         if self.valid_values is not None:
             if value not in self.valid_values:
                 raise ValidationError(value, "valid values: {}".format(
-                    ','.join(self.valid_values)))
+                    ', '.join(self.valid_values)))
             else:
                 return
         else: