diff --git a/hlr/HLR_Tests.ttcn b/hlr/HLR_Tests.ttcn
index 29af522..f7902be 100644
--- a/hlr/HLR_Tests.ttcn
+++ b/hlr/HLR_Tests.ttcn
@@ -995,6 +995,53 @@
 	vc_EUSE.stop;
 }
 
+/**
+ * Test "Structured" Supplementary Services
+ *
+ * NOTE: at the moment, OsmoHLR doesn't support "structured" SS,
+ * so such requests are being rejected (actually ReturnError
+ * with GSM0480_ERR_CODE_FACILITY_NOT_SUPPORTED).
+ */
+private function f_TC_mo_sss_reject() runs on HLR_ConnHdlr {
+	var SS_FacilityInformation ss_req;
+
+	/* Prepare '*#21#' SS request */
+	ss_req := valueof(ts_SS_FACILITY_INVOKE(
+		invoke_id := 0,
+		op_code := SS_OP_CODE_INTERROGATE_SS,
+		ss_code := '21'O));
+
+	/* Send it towards HLR */
+	GSUP.send(valueof(ts_GSUP_PROC_SS_REQ(
+		g_pars.sub.imsi,
+		g_pars.ussd.sid,
+		OSMO_GSUP_SESSION_STATE_BEGIN,
+		enc_SS_FacilityInformation(ss_req))));
+
+	/* Expect ReturnError with FACILITY_NOT_SUPPORTED */
+	f_SS_expect(g_pars.sub.imsi,
+		g_pars.ussd.sid, OSMO_GSUP_SESSION_STATE_END,
+		tr_SS_FACILITY_RETURN_ERROR(0, 21));
+}
+testcase TC_mo_sss_reject() runs on test_CT {
+	var HLR_ConnHdlrPars pars;
+	var HLR_ConnHdlr vc_conn;
+	var HlrSubscriber sub;
+
+	f_init(false);
+
+	/* Create a random subscriber */
+	sub := valueof(t_Sub2G(f_rnd_imsi('26242'H),
+		'49161'H & f_rnd_hexstring(7, 9), "comp128v1"));
+	pars := valueof(t_Pars_sub(sub));
+	pars.ussd.sid := f_rnd_octstring(4);
+
+	f_vty_subscr_create(VTY, sub);
+	vc_conn := f_start_handler(refers(f_TC_mo_sss_reject), pars);
+	vc_conn.done;
+	f_vty_subscr_delete(VTY, sub);
+}
+
 
 /* TODO USSD:
    * MO USSD for IMSI of non-existant subscriber
@@ -1035,6 +1082,9 @@
 	execute( TC_mo_ussd_euse() );
 	execute( TC_mo_ussd_euse_continue() );
 	execute( TC_mo_ussd_euse_defaultroute() );
+
+	/* "Structured" Supplementary Services */
+	execute( TC_mo_sss_reject() );
 };
 
 };
diff --git a/hlr/expected-results.xml b/hlr/expected-results.xml
index 5431b78..8a1ed26 100644
--- a/hlr/expected-results.xml
+++ b/hlr/expected-results.xml
@@ -17,4 +17,5 @@
   <testcase classname='HLR_Tests' name='TC_mo_ussd_euse' time='MASKED'/>
   <testcase classname='HLR_Tests' name='TC_mo_ussd_euse_continue' time='MASKED'/>
   <testcase classname='HLR_Tests' name='TC_mo_ussd_euse_defaultroute' time='MASKED'/>
+  <testcase classname='HLR_Tests' name='TC_mo_sss_reject' time='MASKED'/>
 </testsuite>