diff --git a/bitcoin/psbt.c b/bitcoin/psbt.c
index 015a0eb42..049062765 100644
--- a/bitcoin/psbt.c
+++ b/bitcoin/psbt.c
@@ -821,7 +821,7 @@ void psbt_txid(const tal_t *ctx,
 		wally_tx_free(tx);
 }
 
-struct amount_sat psbt_compute_fee(struct wally_psbt *psbt)
+struct amount_sat psbt_compute_fee(const struct wally_psbt *psbt)
 {
 	struct amount_sat fee, input_amt;
 	struct amount_asset asset;
diff --git a/bitcoin/psbt.h b/bitcoin/psbt.h
index 18b29862a..e1fa9b406 100644
--- a/bitcoin/psbt.h
+++ b/bitcoin/psbt.h
@@ -249,7 +249,7 @@ struct amount_sat psbt_output_get_amount(const struct wally_psbt *psbt,
  *
  * @psbt -psbt
  */
-struct amount_sat psbt_compute_fee(struct wally_psbt *psbt);
+struct amount_sat psbt_compute_fee(const struct wally_psbt *psbt);
 
 /* psbt_has_input - Is this input present on this psbt
  *