diff --git a/src/proxy.c b/src/proxy.c
index c9a038413..234515ddd 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -2174,6 +2174,8 @@ int stream_set_backend(struct stream *s, struct proxy *be)
 				if (s->si[0].wait_event.events)
 					conn->mux->unsubscribe(cs, s->si[0].wait_event.events,
 					    &s->si[0].wait_event);
+				if (conn->mux->flags & MX_FL_NO_UPG)
+					return 0;
 				if (conn_upgrade_mux_fe(conn, cs, &s->req.buf, ist(""), PROTO_MODE_HTTP)  == -1)
 					return 0;