diff --git a/include/openbsc/tlv.h b/include/openbsc/tlv.h
index e215116..453f1d0 100644
--- a/include/openbsc/tlv.h
+++ b/include/openbsc/tlv.h
@@ -110,7 +110,7 @@
 
 struct tlv_p_entry {
 	u_int16_t len;
-	u_int8_t *val;
+	const u_int8_t *val;
 };
 
 enum tlv_type {
@@ -134,7 +134,8 @@
 	struct tlv_p_entry lv[0xff];
 };
 
-int tlv_parse(struct tlv_parsed *dec, const struct tlv_definition *def, u_int8_t *buf, int buf_len);
+int tlv_parse(struct tlv_parsed *dec, const struct tlv_definition *def,
+	      const u_int8_t *buf, int buf_len);
 
 #define TLVP_PRESENT(x, y)	((x)->lv[y].val)
 #define TLVP_LEN(x, y)		(x)->lv[y].len