diff --git a/include/osmocom/codec/codec.h b/include/osmocom/codec/codec.h
index fb127b5..05da911 100644
--- a/include/osmocom/codec/codec.h
+++ b/include/osmocom/codec/codec.h
@@ -63,8 +63,8 @@
 	}
 }
 
-bool osmo_fr_check_sid(uint8_t *rtp_payload, size_t payload_len);
-bool osmo_hr_check_sid(uint8_t *rtp_payload, size_t payload_len);
+bool osmo_fr_check_sid(const uint8_t *rtp_payload, size_t payload_len);
+bool osmo_hr_check_sid(const uint8_t *rtp_payload, size_t payload_len);
 int osmo_amr_rtp_enc(uint8_t *payload, uint8_t cmr, enum osmo_amr_type ft,
 		     enum osmo_amr_quality bfi);
 int osmo_amr_rtp_dec(const uint8_t *payload, int payload_len, uint8_t *cmr,