diff --git a/docs/architecture/mirror.rst b/docs/architecture/mirror.rst
--- a/docs/architecture/mirror.rst
+++ b/docs/architecture/mirror.rst
@@ -56,6 +56,7 @@
 
 - `swh.journal.objects.content`
 - `swh.journal.objects.directory`
+- `swh.journal.objects.extid`
 - `swh.journal.objects.metadata_authority`
 - `swh.journal.objects.metadata_fetcher`
 - `swh.journal.objects.origin_visit_status`