diff --git a/csv_export_base/models/res_partner.py b/csv_export_base/models/res_partner.py
index c9800af..da92451 100644
--- a/csv_export_base/models/res_partner.py
+++ b/csv_export_base/models/res_partner.py
@@ -9,6 +9,11 @@
 class ResPartner(models.Model):
     _inherit = "res.partner"
 
+    _sql_constraints = [
+        ('partner_export_reference_unique', 'UNIQUE (export_reference)',
+         'The export reference must be unique!'),
+    ]
+
     def _default_export_reference(self):
         return self.env["ir.sequence"].next_by_code(
             "res.partner.export.reference"