diff --git a/hsmd/hsmd.c b/hsmd/hsmd.c
index 4ea0805c8..0c354a7ed 100644
--- a/hsmd/hsmd.c
+++ b/hsmd/hsmd.c
@@ -122,7 +122,7 @@ static struct io_plan *bad_req_fmt(struct io_conn *conn,
 	char *str;
 
 	va_start(ap, fmt);
-	str = tal_fmt(tmpctx, fmt, ap);
+	str = tal_vfmt(tmpctx, fmt, ap);
 	va_end(ap);
 
 	/*~ If the client was actually lightningd, it's Game Over; we actually