diff --git a/account_statement_ext/voucher.py b/account_statement_ext/voucher.py
new file mode 100644
index 00000000..2aeee0ac
--- /dev/null
+++ b/account_statement_ext/voucher.py
@@ -0,0 +1,51 @@
+# -*- coding: utf-8 -*-
+##############################################################################
+#
+#    Author: Joel Grand-Guillaume
+#    Copyright 2011-2012 Camptocamp SA
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU Affero General Public License as
+#    published by the Free Software Foundation, either version 3 of the
+#    License, or (at your option) any later version.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU Affero General Public License for more details.
+#
+#    You should have received a copy of the GNU Affero General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+##############################################################################
+
+from openerp.osv.orm import Model
+
+
+class AccountVoucher(Model):
+
+    _inherit = 'account.voucher'
+
+    def _get_period(self, cr, uid, context=None):
+        """If period not in context, take it from the move lines"""
+        if context is None:
+            context = {}
+        if not context.get('period_id') and context.get('move_line_ids'):
+            res = self.pool.get('account.move.line').browse(
+                    cr, uid, context.get('move_line_ids'), context=context)[0].period_id.id
+            context['period_id'] = res
+        elif context.get('date'):
+            periods = self.pool.get('account.period').find(
+                    cr, uid, dt=context['date'], context=context)
+            if periods:
+                context['period_id'] = periods[0]
+        return super(AccountVoucher, self)._get_period(cr, uid, context)
+
+    def create(self, cr, uid, values, context=None):
+        """If no period defined in values, ask it from moves."""
+        if context is None:
+            context = {}
+        if not values.get('period_id'):
+            ctx = dict(context, date=values.get('date'))
+            values['period_id'] = self._get_period(cr, uid, ctx)
+        return super(AccountVoucher, self).create(cr, uid, values, context)