diff --git a/swh/lister/core/tasks.py b/swh/lister/core/tasks.py
index 5d4e0f6..be2ee4f 100644
--- a/swh/lister/core/tasks.py
+++ b/swh/lister/core/tasks.py
@@ -1,73 +1,72 @@
 # Copyright (C) 2017 the Software Heritage developers
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import abc
 import random
 
 from celery import group
-from celery.app.task import TaskType
 
-from swh.scheduler.task import Task
+from swh.scheduler.task import Task, TaskType
 
 from .abstractattribute import AbstractAttribute
 
 
 class AbstractTaskMeta(abc.ABCMeta, TaskType):
     pass
 
 
 class ListerTaskBase(Task, metaclass=AbstractTaskMeta):
     """Lister Tasks define the process of periodically requesting batches of
         repository information from source code hosting services. They
         instantiate Listers to do batches of work at periodic intervals.
 
         There are two main kinds of lister tasks:
 
         1. Discovering new repositories.
         2. Refreshing the list of already discovered repositories.
 
         If the hosting service is indexable (according to the requirements of
         :class:`SWHIndexingLister`), then we can optionally partition the
         set of known repositories into sub-sets to distribute the work.
 
         This means that there is a third possible Task type for Indexing
         Listers:
 
         3. Discover or refresh a specific range of indices.
 
     """
     task_queue = AbstractAttribute('Celery Task queue name')
 
     @abc.abstractmethod
     def new_lister(self):
         """Return a new lister of the appropriate type.
         """
         pass
 
     @abc.abstractmethod
     def run_task(self):
         pass
 
 
 class IndexingDiscoveryListerTask(ListerTaskBase):
     def run_task(self):
         lister = self.new_lister()
         return lister.run(min_index=lister.db_last_index(), max_index=None)
 
 
 class IndexingRangeListerTask(ListerTaskBase):
     def run_task(self, start, end):
         lister = self.new_lister()
         return lister.run(min_index=start, max_index=end)
 
 
 class IndexingRefreshListerTask(ListerTaskBase):
     GROUP_SPLIT = 10000
 
     def run_task(self):
         lister = self.new_lister()
         ranges = lister.db_partition_indices(self.GROUP_SPLIT)
         random.shuffle(ranges)
         range_task = IndexingRangeListerTask()
         group(range_task.s(minv, maxv) for minv, maxv in ranges)()