diff --git a/addons/payment/models/payment_acquirer.py b/addons/payment/models/payment_acquirer.py
index e0a7eb61305..0e3e3b0fb5c 100644
--- a/addons/payment/models/payment_acquirer.py
+++ b/addons/payment/models/payment_acquirer.py
@@ -527,7 +527,7 @@ class PaymentTransaction(models.Model):
         ref_suffix = 1
         init_ref = reference
         while self.env['payment.transaction'].sudo().search_count([('reference', '=', reference)]):
-            reference = init_ref + '-' + str(ref_suffix)
+            reference = init_ref + 'x' + str(ref_suffix)
             ref_suffix += 1
         return reference
 
diff --git a/addons/website_sale/models/sale_order.py b/addons/website_sale/models/sale_order.py
index d845f65ae2a..b95b1afcffd 100644
--- a/addons/website_sale/models/sale_order.py
+++ b/addons/website_sale/models/sale_order.py
@@ -463,7 +463,15 @@ class Website(models.Model):
         tx_id = request.session.get('sale_transaction_id')
         if tx_id:
             transaction = self.env['payment.transaction'].sudo().browse(tx_id)
-            if transaction.state != 'cancel':
+            # Ugly hack for SIPS: SIPS does not allow to reuse a payment reference, even if the
+            # payment was not not proceeded. For example:
+            # - Select SIPS for payment
+            # - Be redirected to SIPS website
+            # - Go back to eCommerce without paying
+            # - Be redirected to SIPS website again => error
+            # Since there is no link module between 'website_sale' and 'payment_sips', we prevent
+            # here to reuse any previous transaction for SIPS.
+            if transaction.state != 'cancel' and transaction.acquirer_id.provider != 'sips':
                 return transaction
             else:
                 request.session['sale_transaction_id'] = False