diff --git a/src/gsm/gsm0808_utils.c b/src/gsm/gsm0808_utils.c
index 4b2a5f5..0d6938e 100644
--- a/src/gsm/gsm0808_utils.c
+++ b/src/gsm/gsm0808_utils.c
@@ -1166,7 +1166,7 @@
  *  \param[in] cfg AMR configuration in GSM 04.08 format.
  *  \param[in] hint if the resulting configuration shall be used with a FR or HR TCH.
  *  \returns configuration bits (S0-S15) */
-uint16_t gsm0808_sc_cfg_from_gsm48_mr_cfg(struct gsm48_multi_rate_conf *cfg,
+uint16_t gsm0808_sc_cfg_from_gsm48_mr_cfg(const struct gsm48_multi_rate_conf *cfg,
 					  bool fr)
 {
 	uint16_t s15_s0 = 0;