diff --git a/odoo/addons/base/models/ir_model.py b/odoo/addons/base/models/ir_model.py
index 7d7a93d7f87..76477936439 100644
--- a/odoo/addons/base/models/ir_model.py
+++ b/odoo/addons/base/models/ir_model.py
@@ -308,7 +308,7 @@ class IrModel(models.Model):
         # clean up registry first
         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]
+            del self.pool[name]
         # add manual models
         cr = self.env.cr
         cr.execute('SELECT * FROM ir_model WHERE state=%s', ['manual'])
diff --git a/odoo/modules/registry.py b/odoo/modules/registry.py
index dc03d0b24d3..ddb1631ec51 100644
--- a/odoo/modules/registry.py
+++ b/odoo/modules/registry.py
@@ -183,6 +183,13 @@ class Registry(Mapping):
         """ Add or replace a model in the registry."""
         self.models[model_name] = model
 
+    def __delitem__(self, model_name):
+        """ Remove a (custom) model from the registry. """
+        del self.models[model_name]
+        # the custom model can inherit from mixins ('mail.thread', ...)
+        for Model in self.models.values():
+            Model._inherit_children.discard(model_name)
+
     def descendants(self, model_names, *kinds):
         """ Return the models corresponding to ``model_names`` and all those
         that inherit/inherits from them.