diff --git a/src/rds.c b/src/rds.c
index cfe72d3..24df250 100644
--- a/src/rds.c
+++ b/src/rds.c
@@ -21,7 +21,7 @@ uint8_t get_rds_custom_groups(RDSEncoder* enc, RDSGroup *group);
 uint8_t get_rds_custom_groups2(RDSEncoder* enc, RDSGroup *group);
 int get_rdsp_lua_group(RDSGroup *group, const char grp);
 
-void get_rds_sequence_group(RDSEncoder* enc, RDSGroup *group, uint8_t good_group, char* grp) {
+void get_rds_sequence_group(RDSEncoder* enc, RDSGroup *group, uint8_t good_group, const char* grp) {
 	if(good_group == 0) {
 		if(get_rdsp_lua_group(group, *grp) == 0) get_rds_ps_group(enc, group);
 		return;
diff --git a/src/rds.h b/src/rds.h
index 48df471..061cc77 100644
--- a/src/rds.h
+++ b/src/rds.h
@@ -159,7 +159,7 @@ void set_rds_defaults(RDSEncoder* enc, uint8_t program);
 void init_rds_encoder(RDSEncoder* enc);
 void add_checkwords(RDSGroup *group, uint8_t *bits);
 uint8_t check_rds_good_group(RDSEncoder* enc, const char* grp);
-void get_rds_sequence_group(RDSEncoder* enc, RDSGroup *group, uint8_t good_group, char* grp);
+void get_rds_sequence_group(RDSEncoder* enc, RDSGroup *group, uint8_t good_group, const char* grp);
 void get_rds_group(RDSEncoder* enc, RDSGroup *group, uint8_t stream);
 void get_rds_bits(RDSEncoder* enc, uint8_t *bits, uint8_t stream);