diff --git a/addons/account/models/account_invoice.py b/addons/account/models/account_invoice.py
index 4828aa333c7..a2ea2ff697d 100644
--- a/addons/account/models/account_invoice.py
+++ b/addons/account/models/account_invoice.py
@@ -750,6 +750,12 @@ class AccountInvoice(models.Model):
 
     @api.multi
     def invoice_validate(self):
+        for invoice in self:
+            #refuse to validate a vendor bill/refund if there already exists one with the same reference for the same partner,
+            #because it's probably a double encoding of the same bill/refund
+            if invoice.type in ('in_invoice', 'in_refund') and invoice.reference:
+                if self.search([('type', 'in', ('in_invoice', 'in_refund')), ('reference', '=', invoice.reference), ('company_id', '=', invoice.company_id.id), ('commercial_partner_id', '=', invoice.commercial_partner_id.id), ('id', '!=', invoice.id)]):
+                    raise UserError(_("Duplicated vendor reference detected. You probably encoded twice the same vendor bill/refund."))
         return self.write({'state': 'open'})
 
     @api.model