--- x/drivers/tty/n_gsm.c
+++ y/drivers/tty/n_gsm.c
@@ -2487,6 +2487,7 @@ static void gsm_cleanup_mux(struct gsm_m
 	gsm->dead = true;
 	mutex_lock(&gsm->mutex);
 
+	dlci = gsm->dlci[0];
 	if (dlci) {
 		if (disc && dlci->state != DLCI_CLOSED) {
 			gsm_dlci_begin_close(dlci);
@@ -2508,8 +2509,10 @@ static void gsm_cleanup_mux(struct gsm_m
 		gsm->has_devices = false;
 	}
 	for (i = NUM_DLCI - 1; i >= 0; i--)
-		if (gsm->dlci[i])
+		if (gsm->dlci[i]) {
 			gsm_dlci_release(gsm->dlci[i]);
+			gsm->dlci[i] = NULL;
+		}
 	mutex_unlock(&gsm->mutex);
 	/* Now wipe the queues */
 	tty_ldisc_flush(gsm->tty);