diff --git a/src/gsm/gsm0502.c b/src/gsm/gsm0502.c
index 94db94e..b147406 100644
--- a/src/gsm/gsm0502.c
+++ b/src/gsm/gsm0502.c
@@ -34,7 +34,7 @@
 #include <inttypes.h>
 
 unsigned int
-gsm0502_calc_paging_group(struct gsm48_control_channel_descr *chan_desc, uint64_t imsi)
+gsm0502_calc_paging_group(const struct gsm48_control_channel_descr *chan_desc, uint64_t imsi)
 {
 	int ccch_conf;
 	int bs_cc_chans;
diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index 30bba91..c5fe550 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -1361,7 +1361,7 @@
  *  Uses From Table 10.5.33 of GSM 04.08 to determine the number of
  *  paging sub-channels in the given control channel configuration
  */
-int gsm48_number_of_paging_subchannels(struct gsm48_control_channel_descr *chan_desc)
+int gsm48_number_of_paging_subchannels(const struct gsm48_control_channel_descr *chan_desc)
 {
 	unsigned int n_pag_blocks = gsm0502_get_n_pag_blocks(chan_desc);