diff --git a/src/osmo-bts-trx/sched_lchan_tchh.c b/src/osmo-bts-trx/sched_lchan_tchh.c
index b6d83d031..d2ee4f058 100644
--- a/src/osmo-bts-trx/sched_lchan_tchh.c
+++ b/src/osmo-bts-trx/sched_lchan_tchh.c
@@ -147,8 +147,10 @@ int rx_tchh_fn(struct l1sched_ts *l1ts, const struct trx_ul_burst_ind *bi)
 		 */
 		rc = gsm0503_tch_hr_decode(tch_data, *bursts_p,
 			fn_is_odd, &n_errors, &n_bits_total);
-		if (rc == (GSM_HR_BYTES + 1)) /* only for valid *speech* frames */
-			lchan_set_marker(osmo_hr_check_sid(tch_data, rc), lchan); /* DTXu */
+		if (rc == (GSM_HR_BYTES + 1)) { /* only for valid *speech* frames */
+			/* gsm0503_tch_hr_decode() prepends a ToC octet (see RFC5993), skip it */
+			lchan_set_marker(osmo_hr_check_sid(&tch_data[1], GSM_HR_BYTES), lchan); /* DTXu */
+		}
 		break;
 	case GSM48_CMODE_SPEECH_AMR: /* AMR */
 		/* the first FN 0,8,17 or 1,9,18 defines that CMI is included