diff --git a/README.rst b/README.rst
index 83d5baa..53341d7 100644
--- a/README.rst
+++ b/README.rst
@@ -9,7 +9,7 @@ pip install mds-cashbook
 
 Requires
 ========
-- Tryton 6.0
+- Tryton 6.8
 
 How to
 ======
@@ -153,6 +153,10 @@ currency are converted  into the display currency of the parent cash book.
 Changes
 =======
 
-*6.0.0 - 05.08.2022*
+*6.8.29 - 24.07.2023*
+
+- fix: type of indexes
+
+*6.8.28 - 05.06.2023*
 
 - init
diff --git a/line.py b/line.py
index 18cbb3e..6a202f5 100644
--- a/line.py
+++ b/line.py
@@ -245,7 +245,7 @@ class Line(SecondCurrencyMixin, MemCacheIndexMx, Workflow, ModelSQL, ModelView):
                 (t.state, Index.Equality())),
             Index(
                 t,
-                (t.reference, Index.Range())),
+                (t.reference, Index.Equality())),
             })
         cls._sql_constraints.extend([
             ('state_val2',
diff --git a/setup.py b/setup.py
index ff59617..0552dca 100644
--- a/setup.py
+++ b/setup.py
@@ -40,7 +40,7 @@ with open(path.join(here, 'versiondep.txt'), encoding='utf-8') as f:
 
 # tryton-version
 major_version = 6
-minor_version = 0
+minor_version = 8
 
 requires = ['python-slugify']
 for dep in info.get('depends', []):
@@ -89,6 +89,7 @@ setup(name='%s_%s' % (PREFIX, MODULE),
     'License :: OSI Approved :: GNU General Public License (GPL)',
     'Programming Language :: Python :: 3.7',
     'Programming Language :: Python :: 3.8',
+    'Programming Language :: Python :: 3.9',
     ],
 
     keywords='tryton cashbook',
diff --git a/tryton.cfg b/tryton.cfg
index ea57ba7..f020b81 100644
--- a/tryton.cfg
+++ b/tryton.cfg
@@ -1,5 +1,5 @@
 [tryton]
-version=6.0.0
+version=6.8.29
 depends:
     res
     currency
diff --git a/types.py b/types.py
index 1217adf..42bb54d 100644
--- a/types.py
+++ b/types.py
@@ -3,7 +3,7 @@
 # The COPYRIGHT file at the top level of this repository contains the
 # full copyright notices and license terms.
 
-from trytond.model import ModelView, ModelSQL, fields, Unique
+from trytond.model import ModelView, ModelSQL, fields, Unique, Index
 from trytond.transaction import Transaction
 from trytond.i18n import gettext
 
@@ -30,6 +30,11 @@ class Type(ModelSQL, ModelView):
         cls._sql_constraints.extend([
             ('code_uniq', Unique(t, t.short), 'cashbook.msg_type_short_unique'),
             ])
+        cls._sql_indexes.update({
+            Index(
+                t,
+                (t.feature, Index.Equality())),
+            })
 
     @classmethod
     def default_feature(cls):