diff --git a/swh/indexer/orchestrator.py b/swh/indexer/orchestrator.py
index 483f3cf..f799283 100644
--- a/swh/indexer/orchestrator.py
+++ b/swh/indexer/orchestrator.py
@@ -1,80 +1,90 @@
 # Copyright (C) 2016  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 random
 
+from celery import group
+
 from swh.core.config import SWHConfig
 from swh.scheduler.celery_backend.config import app
-
 from . import TASK_NAMES, INDEXER_CLASSES
 
 
 class BaseOrchestratorIndexer(SWHConfig):
     """The indexer orchestrator is in charge of:
     - reading batch of contents (list of sha1s as bytes)
     - according to its configuration, filter or not the contents
     - and then broadcast those contents to indexers
 
     """
     CONFIG_BASE_FILENAME = 'indexer/orchestrator'
 
     DEFAULT_CONFIG = {
         'indexers': ('[str]', ['mimetype']),
         'check_presence': ('bool', 'true'),
     }
 
     def __init__(self):
         super().__init__()
         self.config = self.parse_config_file()
         indexer_names = self.config['indexers']
         random.shuffle(indexer_names)
         self.indexers = {
             TASK_NAMES[name]: INDEXER_CLASSES[name]
             for name in indexer_names
         }
         self.check_presence = self.config['check_presence']
 
     def run_with_check(self, sha1s):
         """Run with checking the presence on sha1s in db.
 
         """
+        celery_tasks = []
         for task_name, indexer_class in self.indexers.items():
             indexer = indexer_class()
 
             # filter the contents per indexers
             sha1s_filtered = list(indexer.filter_contents(sha1s))
 
             if not sha1s_filtered:
                 continue
 
-            # send message for indexer to compute and store results
-            app.tasks[task_name].delay(sha1s_filtered)
+            celery_task = app.tasks[task_name].s(sha1s_filtered)
+            celery_tasks.append(celery_task)
+
+        return celery_tasks
 
     def run_no_check(self, sha1s):
         """Simply broadcase sha1s to the indexers' queue.
 
         """
+        celery_tasks = []
         for task_name, _ in self.indexers.items():
             # send message for indexer to compute and store results
-            app.tasks[task_name].delay(sha1s)
+            celery_task = app.tasks[task_name].s(sha1s)
+            celery_tasks.append(celery_task)
+
+        return celery_tasks
 
     def run(self, sha1s):
         if self.check_presence:
-            self.run_with_check(sha1s)
+            celery_tasks = self.run_with_check(sha1s)
         else:
-            self.run_no_check(sha1s)
+            celery_tasks = self.run_no_check(sha1s)
+
+        group(celery_tasks).delay()
 
 
 class OrchestratorAllContentsIndexer(BaseOrchestratorIndexer):
     """Orchestrator which deals with batch of any types of contents.
 
     """
 
 
 class OrchestratorTextContentsIndexer(BaseOrchestratorIndexer):
     """Orchestrator which deals with batch of text contents.
 
     """
     CONFIG_BASE_FILENAME = 'indexer/orchestrator_text'