diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index d6f95f6..7c77613 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -394,7 +394,7 @@
 
 void set_ts_e1link(struct gsm_bts_trx_ts *ts, u_int8_t e1_nr,
 		   u_int8_t e1_ts, u_int8_t e1_ts_ss);
-enum gsm_bts_type parse_btstype(char *arg);
+enum gsm_bts_type parse_btstype(const char *arg);
 const char *btstype2str(enum gsm_bts_type type);
 struct gsm_bts *gsm_bts_by_lac(struct gsm_network *net, unsigned int lac,
 				struct gsm_bts *start_bts);
diff --git a/openbsc/src/gsm_data.c b/openbsc/src/gsm_data.c
index 0ed0845..370c410 100644
--- a/openbsc/src/gsm_data.c
+++ b/openbsc/src/gsm_data.c
@@ -234,7 +234,7 @@
 	[GSM_BTS_TYPE_NANOBTS_1800] = "nanobts1800",
 };
 
-enum gsm_bts_type parse_btstype(char *arg)
+enum gsm_bts_type parse_btstype(const char *arg)
 {
 	int i;
 	for (i = 0; i < ARRAY_SIZE(bts_types); i++) {