diff --git a/addons/sms/models/mail_thread.py b/addons/sms/models/mail_thread.py
index 6ac839e5201..d1cbe67ba38 100644
--- a/addons/sms/models/mail_thread.py
+++ b/addons/sms/models/mail_thread.py
@@ -275,13 +275,14 @@ class MailThread(models.AbstractModel):
                 self._phone_format(number=sms_number) or sms_number
                 for sms_number in sms_numbers
             ]
+            existing_partners_numbers = {vals_dict['number'] for vals_dict in sms_create_vals}
             sms_create_vals += [dict(
                 sms_base_vals,
                 partner_id=False,
                 number=n,
                 state='outgoing' if n else 'error',
                 failure_type='' if n else 'sms_number_missing',
-            ) for n in tocreate_numbers]
+            ) for n in tocreate_numbers if n not in existing_partners_numbers]
 
         # create sms and notification
         existing_pids, existing_numbers = [], []
diff --git a/addons/test_mail_sms/tests/test_sms_post.py b/addons/test_mail_sms/tests/test_sms_post.py
index c8f9daeeb0e..888c8a72690 100644
--- a/addons/test_mail_sms/tests/test_sms_post.py
+++ b/addons/test_mail_sms/tests/test_sms_post.py
@@ -57,6 +57,24 @@ class TestSMSPost(SMSCommon, TestSMSRecipients, CronMixinCase):
 
         self.assertSMSNotification([{'partner': self.partner_1}, {'number': self.random_numbers_san[0]}, {'number': self.random_numbers_san[1]}], self._test_body, messages)
 
+    def test_message_sms_internals_sms_numbers_duplicate(self):
+        """ _message_sms ( which uses _notify_thread_by_sms) allows for specifying additional number to send sms to
+            This test checks for situation where this additional number is the same as partner telephone number.
+            In that case sms shall NOT be sent twice."""
+        with self.with_user('employee'), self.mockSMSGateway():
+            test_record = self.env['mail.test.sms'].browse(self.test_record.id)
+            additional_number_same_as_partner_number = self.partner_1.mobile
+            subtype_id = self.env['ir.model.data']._xmlid_to_res_id('mail.mt_note')
+            test_record._message_sms(
+                body=self._test_body,
+                partner_ids=self.partner_1.ids,
+                subtype_id=subtype_id,
+                sms_numbers=[additional_number_same_as_partner_number],
+                number_field='mobile'
+            )
+        self.assertEqual(len(self._new_sms.filtered(lambda s: s.number == self.partner_numbers[0])), 1,
+            "There should be one message sent if additional number is the same as partner number")
+
     def test_message_sms_internals_subtype(self):
         with self.with_user('employee'), self.mockSMSGateway():
             test_record = self.env['mail.test.sms'].browse(self.test_record.id)