diff --git a/include/openbsc/gsm_subscriber.h b/include/openbsc/gsm_subscriber.h
index 8dcde3e..e0c621b 100644
--- a/include/openbsc/gsm_subscriber.h
+++ b/include/openbsc/gsm_subscriber.h
@@ -28,12 +28,14 @@
 enum gsm_subscriber_field {
 	GSM_SUBSCRIBER_IMSI,
 	GSM_SUBSCRIBER_TMSI,
+	GSM_SUBSCRIBER_EXTENSION,
 };
 
 struct gsm_subscriber *subscr_get(struct gsm_subscriber *subscr);
 struct gsm_subscriber *subscr_put(struct gsm_subscriber *subscr);
 struct gsm_subscriber *subscr_get_by_tmsi(const char *tmsi);
 struct gsm_subscriber *subscr_get_by_imsi(const char *imsi);
+struct gsm_subscriber *subscr_get_by_extension(const char *ext);
 int subscr_update(struct gsm_subscriber *s, struct gsm_bts *bts);
 
 /* internal */