diff --git a/swh/core/scheduling.py b/swh/core/scheduling.py
index 8c4f52b..c3e7e1a 100644
--- a/swh/core/scheduling.py
+++ b/swh/core/scheduling.py
@@ -1,20 +1,23 @@
 # Copyright (C) 2015  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import celery
 
 
 class Task(celery.Task):
     """a schedulable task (abstract class)
 
     Sub-classes must implement the run() method
 
     Current implementation is based on Celery. See
     http://docs.celeryproject.org/en/latest/reference/celery.app.task.html for
     how to use tasks once instantiated
 
     """
+
+    abstract = True
+
     def run(self, *args, **kwargs):
         raise NotImplementedError('tasks must implement the run() method')