diff --git a/onchange_helper/models/models.py b/onchange_helper/models/models.py
index 2584ffe55..ab2a2fba7 100644
--- a/onchange_helper/models/models.py
+++ b/onchange_helper/models/models.py
@@ -79,6 +79,12 @@ class Base(models.AbstractModel):
             result = [(5,)]
             for record in value:
                 vals = {}
+                # We have to check first if the record already exists
+                # (only in case of M2M).
+                if field.type == "many2many" and not isinstance(
+                        record.id, models.NewId):
+                    result.append((4, record.id))
+                    continue
                 for name in record._cache:
                     if name in models.LOG_ACCESS_COLUMNS:
                         continue
diff --git a/onchange_helper/tests/test_onchange.py b/onchange_helper/tests/test_onchange.py
index 101a997de..46f7cc646 100644
--- a/onchange_helper/tests/test_onchange.py
+++ b/onchange_helper/tests/test_onchange.py
@@ -3,13 +3,72 @@
 # Copyright 2019 ACSONE SA/NV
 # @author Sébastien BEAU <sebastien.beau@akretion.com>
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
-
 import mock
 import odoo.tests.common as common
+from odoo import api, models
+
+
+class ResPartnerTester(models.Model):
+    _inherit = "res.partner"
+    _name = "res.partner"
+
+    @api.onchange("name")
+    def _onchange_name_test(self):
+        """
+        When the name change, assign every existing partner category
+        on the partner.
+        This onchange is used to test behavior of this module for M2M fields.
+        :return:
+        """
+        self.category_id = self.env['res.partner.category'].search([], limit=2)
 
 
 class TestOnchange(common.TransactionCase):
 
+    def _init_test_model(self, model_cls):
+        model_cls._build_model(self.registry, self.cr)
+        model = self.env[model_cls._name].with_context(todo=[])
+        model._prepare_setup()
+        model._setup_base(partial=False)
+        model._setup_fields(partial=False)
+        model._setup_complete()
+        model._auto_init()
+        model.init()
+        model._auto_end()
+        return model
+
+    def setUp(self):
+        super(TestOnchange, self).setUp()
+        self.registry.enter_test_mode()
+        self.old_cursor = self.cr
+        self.cr = self.registry.cursor()
+        self.env = api.Environment(self.cr, self.uid, {})
+        self.test_model = self._init_test_model(ResPartnerTester)
+
+    def tearDown(self):
+        self.registry.leave_test_mode()
+        self.cr = self.old_cursor
+        self.env = api.Environment(self.cr, self.uid, {})
+        super(TestOnchange, self).tearDown()
+
+    def test_playing_onchange_m2m(self):
+        """
+        Test if the onchange fill correctly M2M fields.
+        :return:
+        """
+        values = {
+            "name": "Balthazar Melchior Gaspard",
+        }
+        expected_categs = self.env['res.partner.category'].search([], limit=2)
+        # We should have some categs for this test
+        self.assertTrue(expected_categs)
+        # We have to ensure categs are into cache. So just load the name.
+        expected_categs.mapped("name")
+        expected_result = [(5,)]
+        expected_result.extend([(4, c.id) for c in expected_categs])
+        result = self.env['res.partner'].play_onchanges(values, values.keys())
+        self.assertEqual(result["category_id"], expected_result)
+
     def test_playing_onchange_on_model(self):
         res_partner = self.env["res.partner"]
         with mock.patch.object(