diff --git a/swh/vault/api/client.py b/swh/vault/api/client.py
--- a/swh/vault/api/client.py
+++ b/swh/vault/api/client.py
@@ -6,7 +6,7 @@
 from swh.model import hashutil
 from swh.core.api import RPCClient
 
-from swh.vault.backend import NotFoundExc
+from swh.vault.exc import NotFoundExc
 
 
 class RemoteVaultClient(RPCClient):
diff --git a/swh/vault/backend.py b/swh/vault/backend.py
--- a/swh/vault/backend.py
+++ b/swh/vault/backend.py
@@ -4,16 +4,18 @@
 # See top-level LICENSE file for more information
 
 import smtplib
+from email.mime.text import MIMEText
+
 import psycopg2.extras
 import psycopg2.pool
 
-from email.mime.text import MIMEText
-
 from swh.core.db import BaseDb
 from swh.core.db.common import db_transaction
 from swh.model import hashutil
 from swh.scheduler.utils import create_oneshot_task_dict
+
 from swh.vault.cookers import get_cooker_cls
+from swh.vault.exc import NotFoundExc
 
 cooking_task_name = "swh.vault.cooking_tasks.SWHCookingTask"
 
@@ -57,12 +59,6 @@
 """
 
 
-class NotFoundExc(Exception):
-    """Bundle was not found."""
-
-    pass
-
-
 def batch_to_bytes(batch):
     return [(obj_type, hashutil.hash_to_bytes(obj_id)) for obj_type, obj_id in batch]
 
diff --git a/swh/vault/exc.py b/swh/vault/exc.py
new file mode 100644
--- /dev/null
+++ b/swh/vault/exc.py
@@ -0,0 +1,8 @@
+# Copyright (C) 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
+
+
+class NotFoundExc(Exception):
+    pass