diff --git a/openbsc/src/gprs/gprs_subscriber.c b/openbsc/src/gprs/gprs_subscriber.c
index 4434324..0009685 100644
--- a/openbsc/src/gprs/gprs_subscriber.c
+++ b/openbsc/src/gprs/gprs_subscriber.c
@@ -514,6 +514,9 @@
 		return -GMM_CAUSE_INV_MAND_INFO;
 	}
 
+	if (!gsup_msg.cause && GPRS_GSUP_IS_MSGT_ERROR(gsup_msg.message_type))
+		gsup_msg.cause = GMM_CAUSE_NET_FAIL;
+
 	subscr = gprs_subscr_get_by_imsi(gsup_msg.imsi);
 
 	if (!subscr) {
diff --git a/openbsc/tests/sgsn/sgsn_test.c b/openbsc/tests/sgsn/sgsn_test.c
index 25e0310..1036e41 100644
--- a/openbsc/tests/sgsn/sgsn_test.c
+++ b/openbsc/tests/sgsn/sgsn_test.c
@@ -451,6 +451,11 @@
 		0x02, 0x01, 0x02, /* IMSI unknown in HLR */
 	};
 
+	static const uint8_t purge_ms_err_no_cause[] = {
+		0x0d,
+		TEST_GSUP_IMSI1_IE,
+	};
+
 	static const uint8_t purge_ms_res[] = {
 		0x0e,
 		TEST_GSUP_IMSI1_IE,
@@ -588,6 +593,11 @@
 			     sizeof(purge_ms_err));
 	OSMO_ASSERT(rc == -GMM_CAUSE_IMSI_UNKNOWN);
 
+	/* Inject PurgeMsErr() GSUP message */
+	rc = rx_gsup_message(purge_ms_err_no_cause,
+			     sizeof(purge_ms_err_no_cause));
+	OSMO_ASSERT(rc == -GMM_CAUSE_NET_FAIL);
+
 	/* Inject InsertSubscrData GSUP message (unknown IMSI) */
 	last_updated_subscr = NULL;
 	rc = rx_gsup_message(insert_data_req, sizeof(insert_data_req));