diff --git a/odoo/addons/base/ir/ir_model.py b/odoo/addons/base/ir/ir_model.py
index 73f1aa10ec2..891d95e5230 100644
--- a/odoo/addons/base/ir/ir_model.py
+++ b/odoo/addons/base/ir/ir_model.py
@@ -279,9 +279,9 @@ class IrModel(models.Model):
     def _add_manual_models(self):
         """ Add extra models to the registry. """
         # clean up registry first
-        for name, model_class in self.pool.items():
-            if model_class._custom:
-                del self.pool.models[name]
+        custom_models = [name for name, model_class in self.pool.items() if model_class._custom]
+        for name in custom_models:
+            del self.pool.models[name]
         # add manual models
         cr = self.env.cr
         cr.execute('SELECT * FROM ir_model WHERE state=%s', ['manual'])