diff --git a/mesh/util.c b/mesh/util.c
index 73f13aa..348401a 100644
--- a/mesh/util.c
+++ b/mesh/util.c
@@ -75,7 +75,7 @@ bool str2hex(const char *str, uint16_t in_len, uint8_t *out,
 	return true;
 }
 
-size_t hex2str(uint8_t *in, size_t in_len, char *out, size_t out_len)
+size_t hex2str(const uint8_t *in, size_t in_len, char *out, size_t out_len)
 {
 	static const char hexdigits[] = "0123456789abcdef";
 	size_t i;
diff --git a/mesh/util.h b/mesh/util.h
index bb417dc..36247ea 100644
--- a/mesh/util.h
+++ b/mesh/util.h
@@ -11,7 +11,7 @@
 uint32_t get_timestamp_secs(void);
 bool str2hex(const char *str, uint16_t in_len, uint8_t *out,
 							uint16_t out_len);
-size_t hex2str(uint8_t *in, size_t in_len, char *out, size_t out_len);
+size_t hex2str(const uint8_t *in, size_t in_len, char *out, size_t out_len);
 void print_packet(const char *label, const void *data, uint16_t size);
 int create_dir(const char *dir_name);
 void del_path(const char *path);