diff --git a/account_move_usability/__init__.py b/account_move_usability/__init__.py
index dae354a..2b477c7 100644
--- a/account_move_usability/__init__.py
+++ b/account_move_usability/__init__.py
@@ -1 +1,3 @@
 # -*- encoding: utf-8 -*-
+
+from . import account_move_line
diff --git a/account_move_usability/account_move_line.py b/account_move_usability/account_move_line.py
new file mode 100644
index 0000000..7bce2eb
--- /dev/null
+++ b/account_move_usability/account_move_line.py
@@ -0,0 +1,37 @@
+# -*- encoding: utf-8 -*-
+##############################################################################
+#
+#    Account Move Usability module for Odoo
+#    Copyright (C) 2015 Akretion (http://www.akretion.com)
+#    @author Alexis de Lattre <alexis.delattre@akretion.com>
+#
+#    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 import models, api
+
+
+class AccountMoveLine(models.Model):
+    _inherit = 'account.move.line'
+
+    @api.onchange('credit')
+    def _credit_onchange(self):
+        if self.credit and self.debit:
+            self.debit = 0
+
+    @api.onchange('debit')
+    def _debit_onchange(self):
+        if self.debit and self.credit:
+            self.credit = 0