diff --git a/attachment_metadata/models/attachment.py b/attachment_metadata/models/attachment.py
index 6fd9d52b0b5..f385810c39a 100644
--- a/attachment_metadata/models/attachment.py
+++ b/attachment_metadata/models/attachment.py
@@ -2,13 +2,15 @@
 #    Copyright (C) 2014 initOS GmbH & Co. KG (<http://www.initos.com>).
 #   @author: Joel Grand-Guillaume @ Camptocamp SA
 # @ 2015 Valentin CHEMIERE @ Akretion
+# © 2016 @author Mourad EL HADJ MIMOUNE <mourad.elhadj.mimoune@akretion.com>
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
-from openerp import models, fields, api, _
-from openerp.exceptions import Warning as UserError
 import hashlib
 from base64 import b64decode
 
+from openerp import models, fields, api, _
+from openerp.exceptions import Warning as UserError
+
 
 class IrAttachmentMetadata(models.Model):
     _name = 'ir.attachment.metadata'
@@ -31,14 +33,18 @@ class IrAttachmentMetadata(models.Model):
         help="The file type determines an import method to be used "
         "to parse and transform data before their import in ERP")
 
-    @api.depends('datas', 'external_hash')
+    @api.depends('datas')
     def _compute_hash(self):
         for attachment in self:
             if attachment.datas:
                 attachment.internal_hash = hashlib.md5(
                     b64decode(attachment.datas)).hexdigest()
+
+    @api.constrains('internal_hash', 'external_hash')
+    def _check_external_hash(self):
+        for attachment in self:
             if attachment.external_hash and\
-               attachment.internal_hash != attachment.external_hash:
+                    attachment.internal_hash != attachment.external_hash:
                 raise UserError(
                     _("File corrupted: Something was wrong with "
                       "the retrieved file, please relaunch the task."))
@@ -49,3 +55,4 @@ def _get_file_type(self):
         The file is just added as an attachement
         """
         return [('basic_import', 'Basic import')]
+
diff --git a/attachment_metadata/tests/__init__.py b/attachment_metadata/tests/__init__.py
new file mode 100644
index 00000000000..42c4530cf78
--- /dev/null
+++ b/attachment_metadata/tests/__init__.py
@@ -0,0 +1 @@
+from . import test_attachment
diff --git a/attachment_metadata/tests/test_attachment.py b/attachment_metadata/tests/test_attachment.py
new file mode 100644
index 00000000000..7a49fe5473d
--- /dev/null
+++ b/attachment_metadata/tests/test_attachment.py
@@ -0,0 +1,36 @@
+# coding: utf-8
+# ©2016 @author Mourad EL HADJ MIMOUNE <mourad.elhadj.mimoune@akretion.com>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+from base64 import b64encode
+import hashlib
+
+import openerp.tests.common as common
+
+
+class TestNewSource(common.TransactionCase):
+    def setUp(self):
+        super(TestNewSource, self).setUp()
+        self.model_attachment = self.env['ir.attachment.metadata']
+
+    def test_attachement_hash(self):
+        ir_attachment_id1 = self.model_attachment.create({
+            'name': 'filename1',
+            'datas': b64encode("Test import1"),
+            'datas_fname': 'filename1',
+            'external_hash': hashlib.md5("Test import1").hexdigest(),
+        })
+        self.assertEqual(ir_attachment_id1.internal_hash,
+                         ir_attachment_id1.external_hash)
+        ir_attachment_id2 = self.model_attachment.create({
+            'name': 'filename2',
+            'datas': b64encode('Test import2'),
+            'datas_fname': 'filename2',
+        })
+        ir_attachment_ids = ir_attachment_id1 | ir_attachment_id2
+
+        ir_attachment_ids.write(
+            {
+                'datas': b64encode('Test import1'),
+            })
+        self.assertEqual(ir_attachment_ids[0].internal_hash,
+                         ir_attachment_ids[0].internal_hash)