diff --git a/include/openbsc/abis_rsl.h b/include/openbsc/abis_rsl.h
index d5bc663..b3318d3 100644
--- a/include/openbsc/abis_rsl.h
+++ b/include/openbsc/abis_rsl.h
@@ -377,6 +377,7 @@
 			      int n_pag_blocks);
 unsigned int n_pag_blocks(int bs_ccch_sdcch_comb, unsigned int bs_ag_blks_res);
 u_int64_t str_to_imsi(const char *imsi_str);
+u_int8_t lchan2chan_nr(struct gsm_lchan *lchan);
 
 /* to be provided by external code */
 int abis_rsl_sendmsg(struct msgb *msg);