diff --git a/line.py b/line.py
index 9497e03..51d95cc 100644
--- a/line.py
+++ b/line.py
@@ -14,9 +14,10 @@ from trytond.i18n import gettext
 from trytond.report import Report
 from trytond.transaction import Transaction
 from trytond.modules.cashbook.line import STATES, DEPENDS
-from trytond.modules.cashbook.const import DEF_NONE
 from .mixin import SecondUomMixin
 
+DEF_NONE = None
+
 STATESQ1 = {
     'invisible': And(
         Eval('feature', '') != 'asset',