diff --git a/complaint.py b/complaint.py
index c4a5f3aa50..ead206e2ee 100644
--- a/complaint.py
+++ b/complaint.py
@@ -4,6 +4,8 @@
 from collections import defaultdict
 from decimal import Decimal
 
+from sql.functions import CharLength
+
 from trytond.i18n import gettext
 from trytond.model import (
     DeactivableMixin, ModelSQL, ModelView, Workflow, fields)
@@ -187,6 +189,11 @@ class Complaint(Workflow, ModelSQL, ModelView):
             'account.invoice.line': ['credit_note'],
             }
 
+    @classmethod
+    def order_number(cls, tables):
+        table, _ = tables[None]
+        return [CharLength(table.number), table.number]
+
     @staticmethod
     def default_date():
         pool = Pool()
diff --git a/setup.py b/setup.py
index 2c2f5449c8..156b336bba 100755
--- a/setup.py
+++ b/setup.py
@@ -58,7 +58,7 @@ else:
 if local_version:
     version += '+' + '.'.join(local_version)
 
-requires = []
+requires = ['python-sql']
 for dep in info.get('depends', []):
     if not re.match(r'(ir|res)(\W|$)', dep):
         requires.append(get_require_version('trytond_%s' % dep))