diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 23b014b8c919..d439afef9212 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2178,8 +2178,10 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
 
 	/* Free up any link layer users and finally the control channel */
 	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);