diff --git a/include/proto/stream_interface.h b/include/proto/stream_interface.h
index 54d9810..c8d0a4c 100644
--- a/include/proto/stream_interface.h
+++ b/include/proto/stream_interface.h
@@ -56,6 +56,7 @@
 int si_cs_recv(struct conn_stream *cs);
 int si_cs_send(struct conn_stream *cs);
 struct task *si_cs_io_cb(struct task *t, void *ctx, unsigned short state);
+void si_update_both(struct stream_interface *si_f, struct stream_interface *si_b);
 
 /* returns the channel which receives data from this stream interface (input channel) */
 static inline struct channel *si_ic(struct stream_interface *si)