diff --git a/include/osmocom/gsm/meas_rep.h b/include/osmocom/gsm/meas_rep.h
index 79f9f06..ba2accd 100644
--- a/include/osmocom/gsm/meas_rep.h
+++ b/include/osmocom/gsm/meas_rep.h
@@ -28,5 +28,5 @@
 	MEAS_REP_UL_RXQUAL_SUB,
 };
 
-size_t gsm0858_rsl_ul_meas_enc(struct gsm_meas_rep_unidir *mru, bool dtxd_used,
+size_t gsm0858_rsl_ul_meas_enc(const struct gsm_meas_rep_unidir *mru, bool dtxd_used,
 			   uint8_t *buf);
diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c
index 07e082d..9125b0e 100644
--- a/src/gsm/gsm_utils.c
+++ b/src/gsm/gsm_utils.c
@@ -493,7 +493,7 @@
  *  \param[out] buf Pre-allocated bufer for storing IE
  *  \returns Number of bytes filled in buf
  */
-size_t gsm0858_rsl_ul_meas_enc(struct gsm_meas_rep_unidir *mru, bool dtxd_used,
+size_t gsm0858_rsl_ul_meas_enc(const struct gsm_meas_rep_unidir *mru, bool dtxd_used,
 			uint8_t *buf)
 {
 	buf[0] = dtxd_used ? (1 << 6) : 0;