diff --git a/tabellio/documents/question.py b/tabellio/documents/question.py
index acc4e66..95b6243 100644
--- a/tabellio/documents/question.py
+++ b/tabellio/documents/question.py
@@ -54,6 +54,10 @@ class IQuestion(form.Schema):
     histolines = schema.List(title=_(u'Historic Lines'),
                              value_type=HistoLine())
 
+    # reserved for PFB
+    related_docs = RelationList(title=_(u'Related Documents'), default=[], required=False,
+                    value_type=RelationChoice(title=_(u'Related Document'), source=ObjPathSourceBinder()))
+
 class Question(Item, BasePublication):
     implements(IQuestion, IHasRelations)