diff --git a/product/ERP5/Document/OpenOrder.py b/product/ERP5/Document/OpenOrder.py
index 180d495b0b2cf75a019bf71fc294be714d3618f8..063528db4ca6b6d7ca007122d71ae8259ca72acd 100644
--- a/product/ERP5/Document/OpenOrder.py
+++ b/product/ERP5/Document/OpenOrder.py
@@ -33,8 +33,9 @@ from AccessControl import ClassSecurityInfo
 from Products.ERP5Type import Permissions, PropertySheet, interfaces
 from Products.ERP5Type.Accessor.Constant import PropertyGetter as ConstantGetter
 from Products.ERP5.Document.Supply import Supply
+from Products.ERP5.Document.Order import Order
 
-class OpenOrder(Supply):
+class OpenOrder(Supply, Order):
   """
     An OpenOrder is a collection of Open Order Lines
 
diff --git a/product/ERP5/Document/OpenOrderCell.py b/product/ERP5/Document/OpenOrderCell.py
index b5ff967e617ded1a93e36f3657312ac3cc9df04a..4e1e9522b80a5f159ad7f4797c2d69d5b1e15e65 100644
--- a/product/ERP5/Document/OpenOrderCell.py
+++ b/product/ERP5/Document/OpenOrderCell.py
@@ -29,11 +29,16 @@
 from AccessControl import ClassSecurityInfo
 from Products.ERP5Type import Permissions, PropertySheet
 from Products.ERP5.Document.SupplyCell import SupplyCell
+from Products.ERP5.Document.OrderCell import OrderCell
 
-class OpenOrderCell(SupplyCell):
+class OpenOrderCell(SupplyCell, OrderCell):
     """
       A OpenOrderCell allows to define specific quantities
       for each variation of a resource in an Open Order Line.
+
+      TODO:
+      - make sure that this should be (or not) a subclass
+        of OrderCell
     """
     meta_type = 'ERP5 Open Order Cell'
     portal_type = 'Open Order Cell'