diff -up openssh-7.4p1/mux.c.controlPath openssh-7.4p1/mux.c

--- openssh-7.4p1/mux.c.controlPath	2017-05-04 14:49:44.629247946 +0200

+++ openssh-7.4p1/mux.c	2017-05-04 14:52:54.955109022 +0200

@@ -1290,6 +1290,12 @@ muxserver_listen(void)

 	oerrno = errno;

 	umask(old_umask);

 	if (muxserver_sock < 0) {

+		if (oerrno == ENAMETOOLONG) {

+			/* the error is already logged from unix_listener() */

+			error("ControlPath %s too long, "

+			    "disabling multiplexing", options.control_path);

+			goto disable_mux_master;

+		}

 		if (oerrno == EINVAL || oerrno == EADDRINUSE) {

 			error("ControlSocket %s already exists, "

 			    "disabling multiplexing", options.control_path);