diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 3197939a363d..22f49033e01c 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -63,6 +63,7 @@
 )
 from synapse.logging.opentracing import (
     log_kv,
+    set_tag,
     start_active_span_from_edu,
     tag_args,
     trace,
@@ -678,6 +679,7 @@ async def on_send_join_request(
         room_id: str,
         caller_supports_partial_state: bool = False,
     ) -> Dict[str, Any]:
+        set_tag("partial_state", caller_supports_partial_state)
         await self._room_member_handler._join_rate_per_room_limiter.ratelimit(  # type: ignore[has-type]
             requester=None,
             key=room_id,