diff --git a/swh/storage/cassandra/storage.py b/swh/storage/cassandra/storage.py
--- a/swh/storage/cassandra/storage.py
+++ b/swh/storage/cassandra/storage.py
@@ -697,8 +697,8 @@
     def snapshot_get_random(self) -> Sha1Git:
         return self._cql_runner.snapshot_get_random().id
 
-    def object_find_by_sha1_git(self, ids):
-        results = {id_: [] for id_ in ids}
+    def object_find_by_sha1_git(self, ids: List[Sha1Git]) -> Dict[Sha1Git, List[Dict]]:
+        results: Dict[Sha1Git, List[Dict]] = {id_: [] for id_ in ids}
         missing_ids = set(ids)
 
         # Mind the order, revision is the most likely one for a given ID,
diff --git a/swh/storage/in_memory.py b/swh/storage/in_memory.py
--- a/swh/storage/in_memory.py
+++ b/swh/storage/in_memory.py
@@ -694,8 +694,8 @@
     def snapshot_get_random(self) -> Sha1Git:
         return random.choice(list(self._snapshots))
 
-    def object_find_by_sha1_git(self, ids):
-        ret = {}
+    def object_find_by_sha1_git(self, ids: List[Sha1Git]) -> Dict[Sha1Git, List[Dict]]:
+        ret: Dict[Sha1Git, List[Dict]] = {}
         for id_ in ids:
             objs = self._objects.get(id_, [])
             ret[id_] = [{"sha1_git": id_, "type": obj[0],} for obj in objs]
diff --git a/swh/storage/interface.py b/swh/storage/interface.py
--- a/swh/storage/interface.py
+++ b/swh/storage/interface.py
@@ -1003,14 +1003,14 @@
         ...
 
     @remote_api_endpoint("object/find_by_sha1_git")
-    def object_find_by_sha1_git(self, ids):
+    def object_find_by_sha1_git(self, ids: List[Sha1Git]) -> Dict[Sha1Git, List[Dict]]:
         """Return the objects found with the given ids.
 
         Args:
             ids: a generator of sha1_gits
 
         Returns:
-            dict: a mapping from id to the list of objects found. Each object
+            A dict from id to the list of objects found for that id. Each object
             found is itself a dict with keys:
 
             - sha1_git: the input id
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -1093,8 +1093,10 @@
 
     @timed
     @db_transaction(statement_timeout=2000)
-    def object_find_by_sha1_git(self, ids, db=None, cur=None):
-        ret = {id: [] for id in ids}
+    def object_find_by_sha1_git(
+        self, ids: List[Sha1Git], db=None, cur=None
+    ) -> Dict[Sha1Git, List[Dict]]:
+        ret: Dict[Sha1Git, List[Dict]] = {id: [] for id in ids}
 
         for retval in db.object_find_by_sha1_git(ids, cur=cur):
             if retval[1]: