diff --git a/openbsc/src/gprs/sgsn_auth.c b/openbsc/src/gprs/sgsn_auth.c
index 41f7c41..d77a021 100644
--- a/openbsc/src/gprs/sgsn_auth.c
+++ b/openbsc/src/gprs/sgsn_auth.c
@@ -257,7 +257,9 @@
 		gsm0408_gprs_access_granted(mmctx);
 		break;
 	case SGSN_AUTH_REJECTED:
-		gmm_cause = subscr ? subscr->sgsn_data->error_cause : 0;
+		gmm_cause =
+			subscr ? subscr->sgsn_data->error_cause :
+			SGSN_ERROR_CAUSE_NONE;
 
 		if (subscr && (subscr->flags & GPRS_SUBSCRIBER_CANCELLED) != 0)
 			gsm0408_gprs_access_cancelled(mmctx, gmm_cause);