diff --git a/swh/storage/cassandra/converters.py b/swh/storage/cassandra/converters.py
--- a/swh/storage/cassandra/converters.py
+++ b/swh/storage/cassandra/converters.py
@@ -45,7 +45,7 @@
         extra_headers = db_to_git_headers(metadata["extra_headers"])
         metadata["extra_headers"] = extra_headers
     return Revision(
-        parents=parents,
+        parents=tuple(parents),
         type=RevisionType(revision.pop("type")),
         metadata=metadata,
         **revision,