diff --git a/swh/scheduler/tests/conftest.py b/swh/scheduler/tests/conftest.py
index c25dce9..d761f9a 100644
--- a/swh/scheduler/tests/conftest.py
+++ b/swh/scheduler/tests/conftest.py
@@ -1,89 +1,93 @@
 import os
 import pytest
 import glob
 from datetime import timedelta
 
-import swh.scheduler.celery_backend.config
+from swh.core.utils import numfile_sortkey as sortkey
+from swh.scheduler import get_scheduler
+from swh.scheduler.tests import SQL_DIR
+
+# make sure we are not fooled by CELERY_ config environment vars
+for var in [x for x in os.environ.keys() if x.startswith('CELERY')]:
+    os.environ.pop(var)
+
+import swh.scheduler.celery_backend.config  # noqa
 # this import is needed here to enforce creation of the celery current app
 # BEFORE the swh_app fixture is called, otherwise the Celery app instance from
 # celery_backend.config becomes the celery.current_app
 
 
-from swh.core.utils import numfile_sortkey as sortkey
-from swh.scheduler import get_scheduler
-from swh.scheduler.tests import SQL_DIR
-
 DUMP_FILES = os.path.join(SQL_DIR, '*.sql')
 
 # celery tasks for testing purpose; tasks themselves should be
 # in swh/scheduler/tests/celery_tasks.py
 TASK_NAMES = ['ping', 'multiping', 'add', 'error']
 
 
 @pytest.fixture(scope='session')
 def celery_enable_logging():
     return True
 
 
 @pytest.fixture(scope='session')
 def celery_includes():
     return [
         'swh.scheduler.tests.tasks',
     ]
 
 
 @pytest.fixture(scope='session')
 def celery_parameters():
     return {
         'task_cls': 'swh.scheduler.task:SWHTask',
         }
 
 
 @pytest.fixture(scope='session')
 def celery_config():
     return {
         'accept_content': ['application/x-msgpack', 'application/json'],
         'task_serializer': 'msgpack',
         'result_serializer': 'msgpack',
         }
 
 
 # override the celery_session_app fixture to monkeypatch the 'main'
 # swh.scheduler.celery_backend.config.app Celery application
 # with the test application.
 @pytest.fixture(scope='session')
 def swh_app(celery_session_app):
     swh.scheduler.celery_backend.config.app = celery_session_app
     yield celery_session_app
 
 
 @pytest.fixture
 def swh_scheduler(request, postgresql_proc, postgresql):
     scheduler_config = {
         'db': 'postgresql://{user}@{host}:{port}/{dbname}'.format(
             host=postgresql_proc.host,
             port=postgresql_proc.port,
             user='postgres',
             dbname='tests')
     }
 
     all_dump_files = sorted(glob.glob(DUMP_FILES), key=sortkey)
 
     cursor = postgresql.cursor()
     for fname in all_dump_files:
         with open(fname) as fobj:
             cursor.execute(fobj.read())
     postgresql.commit()
 
     scheduler = get_scheduler('local', scheduler_config)
     for taskname in TASK_NAMES:
         scheduler.create_task_type({
             'type': 'swh-test-{}'.format(taskname),
             'description': 'The {} testing task'.format(taskname),
             'backend_name': 'swh.scheduler.tests.tasks.{}'.format(taskname),
             'default_interval': timedelta(days=1),
             'min_interval': timedelta(hours=6),
             'max_interval': timedelta(days=12),
         })
 
     return scheduler