if (get_oid(name, &oid))
                return error("commit '%s' not found.", name);
 
-       buf = read_sha1_file(oid.hash, &type, &size);
+       buf = read_object_file(&oid, &type, &size);
        if (!buf)
                return error("%s: unable to read file.", name);
        if (type != OBJ_COMMIT)
                return error("%s: cannot verify a non-commit object of type %s.",
-                               name, typename(type));
+                               name, type_name(type));
 
        ret = run_gpg_verify(&oid, buf, size, flags);