diff --git a/swh/loader/cvs/tasks.py b/swh/loader/cvs/tasks.py
index bd0bfc8..63867dc 100644
--- a/swh/loader/cvs/tasks.py
+++ b/swh/loader/cvs/tasks.py
@@ -1,51 +1,54 @@
 # Copyright (C) 2015-2021  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 from datetime import datetime
 from typing import Optional
 
 from celery import shared_task
 import iso8601
 
 from .loader import CvsLoader
 
 
 def convert_to_datetime(date: Optional[str]) -> Optional[datetime]:
+    if date is None:
+        return None
     try:
+        assert isinstance(date, str)
         return iso8601.parse_date(date)
     except Exception:
         return None
 
 
 @shared_task(name=__name__ + ".LoadCvsRepository")
 def load_cvs(
     *,
     url: str,
     origin_url: Optional[str] = None,
     destination_path: Optional[str] = None,
     swh_revision: Optional[str] = None,
     visit_date: Optional[str] = None,
 ):
     """Import a CVS repository
 
     Args:
         - url: (mandatory) CVS's repository url to ingest data from
         - origin_url: Optional original url override to use as origin reference
             in the archive. If not provided, "url" is used as origin.
         - destination_path: (optional) root directory to
           locally retrieve svn's data
         - swh_revision: (optional) extra revision hex to
           start from. See swh.loader.svn.CvsLoader.process
           docstring
         - visit_date: Optional date to override the visit date
     """
     loader = CvsLoader.from_configfile(
         url=url,
         origin_url=origin_url,
         destination_path=destination_path,
         swh_revision=swh_revision,
         visit_date=convert_to_datetime(visit_date),
     )
     return loader.load()
diff --git a/swh/loader/cvs/tests/test_tasks.py b/swh/loader/cvs/tests/test_tasks.py
new file mode 100644
index 0000000..332c43e
--- /dev/null
+++ b/swh/loader/cvs/tests/test_tasks.py
@@ -0,0 +1,25 @@
+# Copyright (C) 2019-2021  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
+
+from datetime import datetime, timezone
+
+import pytest
+
+from swh.loader.cvs.tasks import convert_to_datetime
+
+
+@pytest.mark.parametrize(
+    "date,expected_result",
+    [
+        (None, None),
+        (
+            "2021-11-23 09:41:02.434195+00:00",
+            datetime(2021, 11, 23, 9, 41, 2, 434195, tzinfo=timezone.utc),
+        ),
+        ("23112021", None,),  # failure to parse
+    ],
+)
+def test_convert_to_datetime(date, expected_result):
+    assert convert_to_datetime(date) == expected_result