diff --git a/tiramisu/option.py b/tiramisu/option.py
index f6a42c2..df7c985 100644
--- a/tiramisu/option.py
+++ b/tiramisu/option.py
@@ -451,8 +451,8 @@ class Option(BaseOption):
             do_validation(value, force_index)
         else:
             if not isinstance(value, list):
-                raise ValueError(_("invalid value {0} for option {1} "
-                                   "which must be a list").format(value,
+                raise ValueError(_("invalid value {0} for option {1} ")
+                                 _("which must be a list").format(value,
                                                                   self._name))
             for index, val in enumerate(value):
                 do_validation(val, index)