diff --git a/doc/migrate/3.4.0-4.0.0/post.py b/doc/migrate/3.4.0-4.0.0/post.py
index ba1c9028f91..f62bd97e98a 100644
--- a/doc/migrate/3.4.0-4.0.0/post.py
+++ b/doc/migrate/3.4.0-4.0.0/post.py
@@ -86,5 +86,12 @@ cr.commit()
 cr.execute("delete from ir_ui_menu where (id not in (select parent_id from ir_ui_menu where parent_id is not null)) and (id not in (select res_id from ir_values where model='ir.ui.menu'))")
 cr.commit()
 
+# ----------------------------------------- #
+# add default value for discount in invoice #
+# ----------------------------------------- #
+
+cr.execute("update account_invoice_line set discount=0.0 where discount is null;")
+cr.commit()
+
 cr.close()