diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index a26e976492..087e3f9046 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -268,12 +268,15 @@ class RoomSendEventRestServlet(TransactionRestServlet):
         if b"ts" in request.args and requester.app_service:
             event_dict["origin_server_ts"] = parse_integer(request, "ts", 0)
 
+        # XXX Horrible hack.
+        prev_event_ids = parse_strings_from_args(request.args, "prev_event_id")
+
         try:
             (
                 event,
                 _,
             ) = await self.event_creation_handler.create_and_send_nonmember_event(
-                requester, event_dict, txn_id=txn_id
+                requester, event_dict, txn_id=txn_id, prev_event_ids=prev_event_ids
             )
             event_id = event.event_id
         except ShadowBanError: