diff --git a/include/osmocom/msc/vlr.h b/include/osmocom/msc/vlr.h
index 0b61a59..9943f15 100644
--- a/include/osmocom/msc/vlr.h
+++ b/include/osmocom/msc/vlr.h
@@ -284,7 +284,7 @@
 int vlr_subscr_rx_auth_resp(struct vlr_subscr *vsub, bool is_r99, bool is_utran,
 			    const uint8_t *res, uint8_t res_len);
 int vlr_subscr_rx_auth_fail(struct vlr_subscr *vsub, const uint8_t *auts);
-int vlr_subscr_tx_auth_fail_rep(struct vlr_subscr *vsub);
+int vlr_subscr_tx_auth_fail_rep(const struct vlr_subscr *vsub);
 void vlr_subscr_rx_ciph_res(struct vlr_subscr *vsub, struct vlr_ciph_result *res);
 int vlr_subscr_rx_tmsi_reall_compl(struct vlr_subscr *vsub);
 int vlr_subscr_rx_imsi_detach(struct vlr_subscr *vsub);