diff --git a/purchase.py b/purchase.py
index 4c25d8d6a1..b1cfa3c586 100644
--- a/purchase.py
+++ b/purchase.py
@@ -1272,6 +1272,8 @@ class ProductSupplier(OSV):
         :param context: the context
         :return: the purchase date
         '''
+        if not product_supplier.delivery_time:
+            return datetime.date.today()
         return date - datetime.timedelta(product_supplier.delivery_time)
 
 ProductSupplier()