diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 7ca779655..c42b73d11 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -266,6 +266,9 @@ def serialize_event(e, time_now_ms, as_client_event=True,
             if txn_id is not None:
                 d["unsigned"]["transaction_id"] = txn_id
 
+    if not is_invite:
+        d["unsigned"].pop("invite_room_state", None)
+
     if as_client_event:
         d = event_format(d)
 
@@ -275,7 +278,4 @@ def serialize_event(e, time_now_ms, as_client_event=True,
             raise TypeError("only_event_fields must be a list of strings")
         d = only_fields(d, only_event_fields)
 
-    if not is_invite:
-        d["unsigned"].pop("invite_room_state", None)
-
     return d