diff --git a/common/json_helpers.c b/common/json_helpers.c
index a304c534a..c1bf03cc9 100644
--- a/common/json_helpers.c
+++ b/common/json_helpers.c
@@ -270,7 +270,7 @@ void json_add_tx(struct json_stream *result,
 
 void json_add_psbt(struct json_stream *stream,
 		   const char *fieldname,
-		   struct wally_psbt *psbt)
+		   const struct wally_psbt *psbt)
 {
 	const char *psbt_b64;
 	psbt_b64 = psbt_to_b64(NULL, psbt);
diff --git a/common/json_helpers.h b/common/json_helpers.h
index 22b5f66f3..ffb5f7f4e 100644
--- a/common/json_helpers.h
+++ b/common/json_helpers.h
@@ -157,6 +157,6 @@ void json_add_tx(struct json_stream *result,
 /* '"fieldname" : "cHNidP8BAJoCAAAAAljo..." or "cHNidP8BAJoCAAAAAljo..." if fieldname is NULL */
 void json_add_psbt(struct json_stream *stream,
 		   const char *fieldname,
-		   struct wally_psbt *psbt);
+		   const struct wally_psbt *psbt);
 
 #endif /* LIGHTNING_COMMON_JSON_HELPERS_H */