diff --git a/odoo/addons/base/models/ir_model.py b/odoo/addons/base/models/ir_model.py
index 65d73325f6c8..49f84e1c3a61 100644
--- a/odoo/addons/base/models/ir_model.py
+++ b/odoo/addons/base/models/ir_model.py
@@ -221,6 +221,8 @@ def unlink(self):
                 # prevent screwing up fields that depend on these models' fields
                 model.field_id._prepare_update()
 
+        # OpenUpgrade: always remove relations to this model (fix issue #3649)
+        self.env['ir.model.relation'].search([('model', 'in', self.ids)]).unlink()
         # delete fields whose comodel is being removed
         self.env['ir.model.fields'].search([('relation', 'in', self.mapped('model'))]).unlink()