diff --git a/purchase.py b/purchase.py
index 09504608b3..46e45e77b8 100644
--- a/purchase.py
+++ b/purchase.py
@@ -5,6 +5,7 @@ from functools import wraps
 from itertools import groupby
 
 from sql.conditionals import Case
+from sql.functions import CharLength
 
 from trytond.i18n import gettext
 from trytond.model import ModelSQL, ModelView, Workflow, fields
@@ -165,6 +166,11 @@ class Quotation(Workflow, ModelSQL, ModelView):
                     },
                 })
 
+    @classmethod
+    def order_number(cls, tables):
+        table, _ = tables[None]
+        return [CharLength(table.number), table.number]
+
     @classmethod
     def default_company(cls):
         return Transaction().context.get('company')