diff --git a/swh/loader/mercurial/loader.py b/swh/loader/mercurial/loader.py
--- a/swh/loader/mercurial/loader.py
+++ b/swh/loader/mercurial/loader.py
@@ -25,12 +25,13 @@
 from shutil import rmtree
 from tempfile import mkdtemp
 import time
-from typing import Dict, Iterable, List, Optional
+from typing import Any, Dict, Iterable, List, Optional
 
 import billiard
 from dateutil import parser
 import hglib
 
+from swh.core.config import merge_configs
 from swh.loader.core.loader import DVCSLoader
 from swh.loader.core.utils import clean_dangling_folders
 from swh.model import identifiers
@@ -77,22 +78,21 @@
     pass
 
 
+DEFAULT_CONFIG: Dict[str, Any] = {
+    "bundle_filename": "HG20_none_bundle",
+    "reduce_effort": False,
+    "temp_directory": "/tmp",
+    "cache1_size": 800 * 1024 * 1024,
+    "cache2_size": 800 * 1024 * 1024,
+    "clone_timeout_seconds": 7200,
+}
+
+
 class HgBundle20Loader(DVCSLoader):
     """Mercurial loader able to deal with remote or local repository.
 
     """
 
-    CONFIG_BASE_FILENAME = "loader/mercurial"
-
-    ADDITIONAL_CONFIG = {
-        "bundle_filename": ("str", "HG20_none_bundle"),
-        "reduce_effort": ("bool", False),
-        "temp_directory": ("str", "/tmp"),
-        "cache1_size": ("int", 800 * 1024 * 1024),
-        "cache2_size": ("int", 800 * 1024 * 1024),
-        "clone_timeout_seconds": ("int", 7200),
-    }
-
     visit_type = "hg"
 
     def __init__(
@@ -103,6 +103,7 @@
         logging_class="swh.loader.mercurial.Bundle20Loader",
     ):
         super().__init__(logging_class=logging_class)
+        self.config = merge_configs(DEFAULT_CONFIG, self.config)
         self.origin_url = url
         self.visit_date = visit_date
         self.directory = directory
diff --git a/swh/loader/mercurial/tests/test_tasks.py b/swh/loader/mercurial/tests/test_tasks.py
--- a/swh/loader/mercurial/tests/test_tasks.py
+++ b/swh/loader/mercurial/tests/test_tasks.py
@@ -1,10 +1,12 @@
-# Copyright (C) 2018-2019  The Software Heritage developers
+# Copyright (C) 2018-2020  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
 
 
-def test_loader(mocker, swh_scheduler_celery_app, swh_scheduler_celery_worker):
+def test_loader(
+    mocker, swh_config, swh_scheduler_celery_app, swh_scheduler_celery_worker
+):
     mock_loader = mocker.patch("swh.loader.mercurial.loader.HgBundle20Loader.load")
     mock_loader.return_value = {"status": "eventful"}
 
@@ -21,7 +23,9 @@
     mock_loader.assert_called_once_with()
 
 
-def test_archive_loader(mocker, swh_scheduler_celery_app, swh_scheduler_celery_worker):
+def test_archive_loader(
+    mocker, swh_config, swh_scheduler_celery_app, swh_scheduler_celery_worker
+):
     mock_loader = mocker.patch(
         "swh.loader.mercurial.loader.HgArchiveBundle20Loader.load"
     )