diff --git a/src/libmsc/gsm_09_11.c b/src/libmsc/gsm_09_11.c
index d2ad0b7..c133656 100644
--- a/src/libmsc/gsm_09_11.c
+++ b/src/libmsc/gsm_09_11.c
@@ -51,6 +51,39 @@
 /* FIXME: choose a proper range */
 static uint32_t new_callref = 0x20000001;
 
+static void ncss_session_timeout_handler(void *_trans)
+{
+	struct gsm_trans *trans = (struct gsm_trans *) _trans;
+	struct osmo_gsup_message gsup_msg = { 0 };
+
+	/* The timeout might be disabled from the VTY */
+	if (trans->net->ncss_guard_timeout == 0)
+		return;
+
+	LOGP(DMM, LOGL_NOTICE, "SS/USSD session timeout, releasing "
+		"transaction (trans=%p, callref=%x)\n", trans, trans->callref);
+
+	/* Indicate connection release to subscriber (if active) */
+	if (trans->conn != NULL) {
+		/* This pair of cause location and value is used by commercial networks */
+		msc_send_ussd_release_complete_cause(trans->conn, trans->transaction_id,
+			GSM48_CAUSE_LOC_PUN_S_LU, GSM48_CC_CAUSE_NORMAL_UNSPEC);
+	}
+
+	/* Terminate GSUP session with EUSE */
+	gsup_msg.message_type = OSMO_GSUP_MSGT_PROC_SS_ERROR;
+	OSMO_STRLCPY_ARRAY(gsup_msg.imsi, trans->vsub->imsi);
+
+	gsup_msg.session_state = OSMO_GSUP_SESSION_STATE_END;
+	gsup_msg.session_id = trans->callref;
+	gsup_msg.cause = GMM_CAUSE_NET_FAIL;
+
+	osmo_gsup_client_enc_send(trans->net->vlr->gsup_client, &gsup_msg);
+
+	/* Finally, release this transaction */
+	trans_free(trans);
+}
+
 /* Entry point for call independent MO SS messages */
 int gsm0911_rcv_nc_ss(struct ran_conn *conn, struct msgb *msg)
 {
@@ -108,6 +141,10 @@
 			return -ENOMEM;
 		}
 
+		/* Init inactivity timer */
+		osmo_timer_setup(&trans->ss.timer_guard,
+			ncss_session_timeout_handler, trans);
+
 		/* Count active NC SS/USSD sessions */
 		osmo_counter_inc(conn->network->active_nc_ss);
 
@@ -116,6 +153,12 @@
 		cm_service_request_concludes(conn, msg);
 	}
 
+	/* (Re)schedule the inactivity timer */
+	if (conn->network->ncss_guard_timeout > 0) {
+		osmo_timer_schedule(&trans->ss.timer_guard,
+			conn->network->ncss_guard_timeout, 0);
+	}
+
 	/* Attempt to extract Facility IE */
 	rc = gsm0480_extract_ie_by_tag(gh, msgb_l3len(msg),
 		&facility_ie, &facility_ie_len, GSM0480_IE_FACILITY);
@@ -233,6 +276,12 @@
 		transt->conn = ran_conn_get(conn, RAN_CONN_USE_TRANS_NC_SS);
 		transt->paging_request = NULL;
 
+		/* (Re)schedule the inactivity timer */
+		if (conn->network->ncss_guard_timeout > 0) {
+			osmo_timer_schedule(&transt->ss.timer_guard,
+				conn->network->ncss_guard_timeout, 0);
+		}
+
 		/* Send stored message */
 		ss_msg = transt->ss.msg;
 		gh = (struct gsm48_hdr *) msgb_push(ss_msg, sizeof(*gh));
@@ -317,6 +366,10 @@
 	}
 	trans->transaction_id = tid;
 
+	/* Init inactivity timer */
+	osmo_timer_setup(&trans->ss.timer_guard,
+		ncss_session_timeout_handler, trans);
+
 	/* Attempt to find connection */
 	conn = connection_for_subscr(vsub);
 	if (conn) {
@@ -371,6 +424,9 @@
 	if (trans->ss.msg != NULL)
 		msgb_free(trans->ss.msg);
 
+	/* Stop inactivity timer */
+	osmo_timer_del(&trans->ss.timer_guard);
+
 	/* One session less */
 	osmo_counter_dec(trans->net->active_nc_ss);
 }
@@ -420,6 +476,12 @@
 			return 0;
 	}
 
+	/* (Re)schedule the inactivity timer */
+	if (net->ncss_guard_timeout > 0) {
+		osmo_timer_schedule(&trans->ss.timer_guard,
+			net->ncss_guard_timeout, 0);
+	}
+
 	/* Allocate and prepare a new MT message */
 	ss_msg = gsm48_msgb_alloc_name("GSM 04.08 SS/USSD");
 	gh = (struct gsm48_hdr *) msgb_push(ss_msg, sizeof(*gh));
diff --git a/src/libmsc/msc_vty.c b/src/libmsc/msc_vty.c
index 078b83a..5aa533b 100644
--- a/src/libmsc/msc_vty.c
+++ b/src/libmsc/msc_vty.c
@@ -375,6 +375,18 @@
 		 "mncc-guard-timeout <0-255>",
 		 MNCC_GUARD_TIMEOUT_STR MNCC_GUARD_TIMEOUT_VALUE_STR);
 
+#define NCSS_STR "Configure call independent Supplementary Services\n"
+
+DEFUN(cfg_msc_ncss_guard_timeout,
+      cfg_msc_ncss_guard_timeout_cmd,
+      "ncss guard-timeout <0-255>",
+      NCSS_STR "Set guard timer for session activity\n"
+      "guard timer value (sec.), or 0 to disable\n")
+{
+	gsmnet->ncss_guard_timeout = atoi(argv[0]);
+	return CMD_SUCCESS;
+}
+
 DEFUN(cfg_msc_assign_tmsi, cfg_msc_assign_tmsi_cmd,
       "assign-tmsi",
       "Assign TMSI during Location Updating.\n")
@@ -496,6 +508,8 @@
 		vty_out(vty, " mncc external %s%s", gsmnet->mncc_sock_path, VTY_NEWLINE);
 	vty_out(vty, " mncc guard-timeout %i%s",
 		gsmnet->mncc_guard_timeout, VTY_NEWLINE);
+	vty_out(vty, " ncss guard-timeout %i%s",
+		gsmnet->ncss_guard_timeout, VTY_NEWLINE);
 	vty_out(vty, " %sassign-tmsi%s",
 		gsmnet->vlr->cfg.assign_tmsi? "" : "no ", VTY_NEWLINE);
 
@@ -1588,6 +1602,7 @@
 	install_element(MSC_NODE, &cfg_msc_mncc_external_cmd);
 	install_element(MSC_NODE, &cfg_msc_mncc_guard_timeout_cmd);
 	install_element(MSC_NODE, &cfg_msc_deprecated_mncc_guard_timeout_cmd);
+	install_element(MSC_NODE, &cfg_msc_ncss_guard_timeout_cmd);
 	install_element(MSC_NODE, &cfg_msc_no_assign_tmsi_cmd);
 	install_element(MSC_NODE, &cfg_msc_auth_tuple_max_reuse_count_cmd);
 	install_element(MSC_NODE, &cfg_msc_auth_tuple_reuse_on_error_cmd);
diff --git a/src/libmsc/osmo_msc.c b/src/libmsc/osmo_msc.c
index 9828da1..5c6f0aa 100644
--- a/src/libmsc/osmo_msc.c
+++ b/src/libmsc/osmo_msc.c
@@ -54,6 +54,7 @@
 	net->t3212 = 5;
 
 	net->mncc_guard_timeout = 180;
+	net->ncss_guard_timeout = 30;
 
 	net->paging_response_timer = MSC_PAGING_RESPONSE_TIMER_DEFAULT;