diff --git a/addons/account/models/account_move.py b/addons/account/models/account_move.py
index 5ec7a803ab8..2c3ff5149d6 100644
--- a/addons/account/models/account_move.py
+++ b/addons/account/models/account_move.py
@@ -7,7 +7,6 @@ from odoo.tools.misc import formatLang, format_date
 
 from datetime import date, timedelta
 from itertools import groupby
-from stdnum.iso7064 import mod_97_10
 from itertools import zip_longest
 from hashlib import sha256
 from json import dumps
@@ -24,6 +23,15 @@ INTEGRITY_HASH_MOVE_FIELDS = ('date', 'journal_id', 'company_id')
 INTEGRITY_HASH_LINE_FIELDS = ('debit', 'credit', 'account_id', 'partner_id')
 
 
+def calc_check_digits(number):
+    """Calculate the extra digits that should be appended to the number to make it a valid number.
+    Source: python-stdnum iso7064.mod_97_10.calc_check_digits
+    """
+    number_base10 = ''.join(str(int(x, 36)) for x in number)
+    checksum = int(number_base10) % 97
+    return '%02d' % ((98 - 100 * checksum) % 97)
+
+
 class AccountMove(models.Model):
     _name = "account.move"
     _inherit = ['portal.mixin', 'mail.thread', 'mail.activity.mixin']
@@ -1679,7 +1687,7 @@ class AccountMove(models.Model):
         """
         self.ensure_one()
         base = self.id
-        check_digits = mod_97_10.calc_check_digits('{}RF'.format(base))
+        check_digits = calc_check_digits('{}RF'.format(base))
         reference = 'RF{} {}'.format(check_digits, " ".join(["".join(x) for x in zip_longest(*[iter(str(base))]*4, fillvalue="")]))
         return reference
 
@@ -1698,7 +1706,7 @@ class AccountMove(models.Model):
         partner_ref = self.partner_id.ref
         partner_ref_nr = re.sub('\D', '', partner_ref or '')[-21:] or str(self.partner_id.id)[-21:]
         partner_ref_nr = partner_ref_nr[-21:]
-        check_digits = mod_97_10.calc_check_digits('{}RF'.format(partner_ref_nr))
+        check_digits = calc_check_digits('{}RF'.format(partner_ref_nr))
         reference = 'RF{} {}'.format(check_digits, " ".join(["".join(x) for x in zip_longest(*[iter(partner_ref_nr)]*4, fillvalue="")]))
         return reference