diff --git a/commission.py b/commission.py
index 1398980636..3005376b88 100644
--- a/commission.py
+++ b/commission.py
@@ -10,6 +10,7 @@ try:
 except ImportError:
     Null = None
 from sql.aggregate import Sum
+from sql.conditionals import Case
 
 from trytond.model import ModelView, ModelSQL, MatchMixin, fields
 from trytond.pyson import Eval, Bool, If, Id, PYSONEncoder
@@ -173,7 +174,7 @@ class PlanLines(ModelSQL, ModelView, MatchMixin):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == Null, table.sequence]
+        return [Case((table.sequence == Null, 0), else_=1), table.sequence]
 
     @staticmethod
     def default_formula():