diff --git a/syndicate/relay.rkt b/syndicate/relay.rkt
index 52c2486..e6096ca 100644
--- a/syndicate/relay.rkt
+++ b/syndicate/relay.rkt
@@ -214,6 +214,8 @@
                    local-ref
                    transient?
                    (lambda ()
+                     (when transient?
+                       (error 'rewrite-ref-out* "Cannot send transient reference"))
                      (define oid (tunnel-relay-next-local-oid tr))
                      (set-tunnel-relay-next-local-oid! tr (+ oid 1))
                      (wire-symbol oid local-ref 0))))