diff --git a/swh/vault/cache.py b/swh/vault/cache.py
index 5717d40..bd88b9f 100644
--- a/swh/vault/cache.py
+++ b/swh/vault/cache.py
@@ -1,39 +1,39 @@
 # Copyright (C) 2016-2017  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 swh.model import hashutil
 from swh.model.swhids import CoreSWHID
 from swh.objstorage.factory import get_objstorage
 from swh.objstorage.objstorage import compute_hash
 
 
 class VaultCache:
     """The Vault cache is an object storage that stores Vault bundles.
 
     This implementation computes sha1('<bundle_type>:<swhid>') as the
     internal identifiers used in the underlying objstorage.
     """
 
     def __init__(self, **objstorage):
         self.objstorage = get_objstorage(**objstorage)
 
-    def add(self, bundle_type, swhid: CoreSWHID, content):
+    def add(self, bundle_type, swhid: CoreSWHID, content) -> None:
         sid = self._get_internal_id(bundle_type, swhid)
-        return self.objstorage.add(content, sid)
+        self.objstorage.add(content, sid)
 
-    def get(self, bundle_type, swhid: CoreSWHID):
+    def get(self, bundle_type, swhid: CoreSWHID) -> bytes:
         sid = self._get_internal_id(bundle_type, swhid)
         return self.objstorage.get(hashutil.hash_to_bytes(sid))
 
     def delete(self, bundle_type, swhid: CoreSWHID):
         sid = self._get_internal_id(bundle_type, swhid)
         return self.objstorage.delete(hashutil.hash_to_bytes(sid))
 
-    def is_cached(self, bundle_type, swhid: CoreSWHID):
+    def is_cached(self, bundle_type, swhid: CoreSWHID) -> bool:
         sid = self._get_internal_id(bundle_type, swhid)
         return hashutil.hash_to_bytes(sid) in self.objstorage
 
     def _get_internal_id(self, bundle_type, swhid: CoreSWHID):
         return compute_hash("{}:{}".format(bundle_type, swhid).encode())