diff --git a/purchase.py b/purchase.py
index e2f6bd0a65..66e3f10d3a 100644
--- a/purchase.py
+++ b/purchase.py
@@ -1080,7 +1080,9 @@ class PurchaseLine(ModelSQL, ModelView):
         res['note'] = line.note
         if line.type != 'line':
             return [res]
-        if line.purchase.invoice_method == 'order':
+        if (line.sale.invoice_method == 'order'
+                or not line.product
+                or line.product.type == 'service'):
             quantity = line.quantity
         else:
             quantity = 0.0