diff --git a/openbsc/src/libbsc/gsm_04_08_utils.c b/openbsc/src/libbsc/gsm_04_08_utils.c
index db9dabb..3447d27 100644
--- a/openbsc/src/libbsc/gsm_04_08_utils.c
+++ b/openbsc/src/libbsc/gsm_04_08_utils.c
@@ -378,7 +378,12 @@
 	}
 }
 
-int gsm48_multirate_config(uint8_t *lv, struct amr_multirate_conf *mr, struct amr_mode *modes)
+/*! \brief Encode a TS 04.08 multirate config LV according to 10.5.2.21aa
+ *  \param[out] lv caller-allocated buffer of 7 bytes. First octet is IS length
+ *  \param[in] mr multi-rate configuration to encode
+ *  \param[in] modes array describing the AMR modes
+ *  \returns 0 on success */
+int gsm48_multirate_config(uint8_t *lv, const struct amr_multirate_conf *mr, const struct amr_mode *modes)
 {
 	int num = 0, i;