diff --git a/include/osmocom/codec/ecu.h b/include/osmocom/codec/ecu.h
index f7a29a0..ec0a2f8 100644
--- a/include/osmocom/codec/ecu.h
+++ b/include/osmocom/codec/ecu.h
@@ -11,5 +11,5 @@
 	uint8_t frame_backup[GSM_FR_BYTES];
 };
 
-void osmo_ecu_fr_reset(struct osmo_ecu_fr_state *state, uint8_t *frame);
+void osmo_ecu_fr_reset(struct osmo_ecu_fr_state *state, const uint8_t *frame);
 int osmo_ecu_fr_conceal(struct osmo_ecu_fr_state *state, uint8_t *frame);
diff --git a/src/codec/ecu_fr.c b/src/codec/ecu_fr.c
index 20a0f89..ef42ea9 100644
--- a/src/codec/ecu_fr.c
+++ b/src/codec/ecu_fr.c
@@ -130,7 +130,7 @@
  * \param[in] state The state object for the ECU
  * \param[out] frame The valid frame (GSM_FR_BYTES bytes in RTP payload format)
  */
-void osmo_ecu_fr_reset(struct osmo_ecu_fr_state *state, uint8_t *frame)
+void osmo_ecu_fr_reset(struct osmo_ecu_fr_state *state, const uint8_t *frame)
 {
 	state->subsequent_lost_frame = false;
 	memcpy(state->frame_backup, frame, GSM_FR_BYTES);