diff --git a/doc/manual_installation/modoboa.rst b/doc/manual_installation/modoboa.rst
index 733fd8ad8..1f828be20 100644
--- a/doc/manual_installation/modoboa.rst
+++ b/doc/manual_installation/modoboa.rst
@@ -202,7 +202,7 @@ following content inside::
   0       *       *       *       *       root    $PYTHON $INSTANCE/manage.py communicate_with_public_api
 
   # Generate DKIM keys (they will belong to the user running this job)
-  *       *       *       *       *       root    $PYTHON $INSTANCE/manage.py modo manage_dkim_keys
+  *       *       *       *       *       root    umask 077 && $PYTHON $INSTANCE/manage.py modo manage_dkim_keys
 
 
 Now you can continue to the :ref:`webserver` section.