diff --git a/product.py b/product.py
index 454f2a5728..62df619f17 100644
--- a/product.py
+++ b/product.py
@@ -411,7 +411,7 @@ class ProductSupplier(
         '''
         Date = Pool().get('ir.date')
 
-        if self.lead_time_used is None:
+        if self.lead_time_used is None or date is None:
             return Date.today()
         return date - self.lead_time_used