diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 2294d5b633b5..641980993d6c 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1587,6 +1587,7 @@ static void gsm_dlci_data(struct gsm_dlci *dlci, const u8 *data, int clen)
 			if (len == 0)
 				return;
 		}
+		len--;
 		slen++;
 		tty = tty_port_tty_get(port);
 		if (tty) {