diff --git a/include/osmocom/gsm/gsm0808_utils.h b/include/osmocom/gsm/gsm0808_utils.h
index 0a7429e..8746ceb 100644
--- a/include/osmocom/gsm/gsm0808_utils.h
+++ b/include/osmocom/gsm/gsm0808_utils.h
@@ -104,7 +104,7 @@
 int gsm0808_chan_type_to_speech_codec(uint8_t perm_spch);
 int gsm0808_speech_codec_from_chan_type(struct gsm0808_speech_codec *sc,
 					uint8_t perm_spch);
-uint16_t gsm0808_sc_cfg_from_gsm48_mr_cfg(struct gsm48_multi_rate_conf *cfg, bool fr);
+uint16_t gsm0808_sc_cfg_from_gsm48_mr_cfg(const struct gsm48_multi_rate_conf *cfg, bool fr);
 
 /*! Return 3GPP TS 48.008 3.2.2.49 Current Channel Type 1 from enum gsm_chan_t. */
 static inline uint8_t gsm0808_current_channel_type_1(enum gsm_chan_t type)