diff --git a/include/osmocom/msc/gsm_04_11_gsup.h b/include/osmocom/msc/gsm_04_11_gsup.h
index 4034f5e19..9c8c7cf2a 100644
--- a/include/osmocom/msc/gsm_04_11_gsup.h
+++ b/include/osmocom/msc/gsm_04_11_gsup.h
@@ -12,8 +12,8 @@ int gsm411_gsup_mo_ready_for_sm_req(struct gsm_trans *trans, uint8_t sm_rp_mr);
 int gsm411_gsup_mo_fwd_sm_req(struct gsm_trans *trans, struct msgb *msg,
 	uint8_t sm_rp_mr, uint8_t *sm_rp_da, uint8_t sm_rp_da_len);
 
-int gsm411_gsup_mt_fwd_sm_res(struct gsm_trans *trans, uint8_t sm_rp_mr);
+int gsm411_gsup_mt_fwd_sm_res(struct gsm_trans *trans, uint8_t sm_rp_mr, const uint8_t *ui_buf, uint8_t ui_len);
 int gsm411_gsup_mt_fwd_sm_err(struct gsm_trans *trans,
-	uint8_t sm_rp_mr, uint8_t cause);
+	uint8_t sm_rp_mr, uint8_t cause, const uint8_t *ui_buf, uint8_t ui_len);
 
 int gsm411_gsup_rx(struct gsup_client_mux *gcm, void *data, const struct osmo_gsup_message *gsup_msg);
diff --git a/src/libmsc/gsm_04_11.c b/src/libmsc/gsm_04_11.c
index 6536d0b84..b6d5f4a7b 100644
--- a/src/libmsc/gsm_04_11.c
+++ b/src/libmsc/gsm_04_11.c
@@ -852,7 +852,19 @@ static int gsm411_rx_rp_ack(struct gsm_trans *trans,
 
 	if (trans->net->sms_over_gsup) {
 		/* Forward towards SMSC via GSUP */
-		return gsm411_gsup_mt_fwd_sm_res(trans, rph->msg_ref);
+		uint8_t ui_len = 0;
+		uint8_t *ui_buf = NULL;
+		/* check for:
+		 * - sufficient size for tag, length and data
+		 * - RP-User-Data tag
+		 * - user data length is valid */
+		if (rph->len > 2 &&
+		    rph->data[0] == GSM411_IE_RP_USER_DATA &&
+		    rph->data[1] <= (rph->len - 2)) {
+			ui_len = rph->data[1];
+			ui_buf = &(rph->data[2]);
+		}
+		return gsm411_gsup_mt_fwd_sm_res(trans, rph->msg_ref, ui_buf, ui_len);
 	}
 
 	if (!sms) {
@@ -893,7 +905,23 @@ static int gsm411_rx_rp_error(struct gsm_trans *trans,
 
 	if (trans->net->sms_over_gsup) {
 		/* Forward towards SMSC via GSUP */
-		return gsm411_gsup_mt_fwd_sm_err(trans, rph->msg_ref, cause);
+		uint8_t ui_len = 0;
+		uint8_t *ui_buf = NULL;
+		uint8_t ui_tag_idx = cause_len + 1;
+		uint8_t ui_len_idx = ui_tag_idx + 1;
+		uint8_t ui_buf_idx = ui_len_idx + 1;
+		/* check for:
+		 * - sufficient size for tag, length and data
+		 * - RP-User-Data tag
+		 * - user data length is valid */
+		if (rph->len > ui_buf_idx &&
+		    rph->data[ui_tag_idx] == GSM411_IE_RP_USER_DATA &&
+		    rph->data[ui_len_idx] <= (rph->len - ui_buf_idx)) {
+			ui_len = rph->data[ui_len_idx];
+			ui_buf = &(rph->data[ui_buf_idx]);
+		}
+
+		return gsm411_gsup_mt_fwd_sm_err(trans, rph->msg_ref, cause, ui_buf, ui_len);
 	}
 
 	if (!sms) {
diff --git a/src/libmsc/gsm_04_11_gsup.c b/src/libmsc/gsm_04_11_gsup.c
index 96fdbc648..4dcc3026a 100644
--- a/src/libmsc/gsm_04_11_gsup.c
+++ b/src/libmsc/gsm_04_11_gsup.c
@@ -184,7 +184,7 @@ msg_error:
 	return -EINVAL;
 }
 
-int gsm411_gsup_mt_fwd_sm_res(struct gsm_trans *trans, uint8_t sm_rp_mr)
+int gsm411_gsup_mt_fwd_sm_res(struct gsm_trans *trans, uint8_t sm_rp_mr, const uint8_t *ui_buf, uint8_t ui_len)
 {
 	struct osmo_gsup_message gsup_msg;
 
@@ -202,11 +202,17 @@ int gsm411_gsup_mt_fwd_sm_res(struct gsm_trans *trans, uint8_t sm_rp_mr)
 	gsup_msg.destination_name_len = trans->sms.gsup_source_name_len;
 	gsup_client_mux_tx_set_source(trans->net->gcm, &gsup_msg);
 
+	/* include optional SM-RP-UI field if present */
+	if (ui_len) {
+		gsup_msg.sm_rp_ui_len = ui_len;
+		gsup_msg.sm_rp_ui = ui_buf;
+	}
+
 	return gsup_client_mux_tx(trans->net->gcm, &gsup_msg);
 }
 
 int gsm411_gsup_mt_fwd_sm_err(struct gsm_trans *trans,
-	uint8_t sm_rp_mr, uint8_t cause)
+	uint8_t sm_rp_mr, uint8_t cause, const uint8_t *ui_buf, uint8_t ui_len)
 {
 	struct osmo_gsup_message gsup_msg;
 
@@ -227,7 +233,12 @@ int gsm411_gsup_mt_fwd_sm_err(struct gsm_trans *trans,
 	/* SM-RP-Cause value */
 	gsup_msg.sm_rp_cause = &cause;
 
-	/* TODO: include optional SM-RP-UI field if present */
+	/* include optional SM-RP-UI field if present */
+	if (ui_len) {
+		gsup_msg.sm_rp_ui_len = ui_len;
+		gsup_msg.sm_rp_ui = ui_buf;
+	}
+
 	return gsup_client_mux_tx(trans->net->gcm, &gsup_msg);
 }