--- a/mercurial/cext/pathencode.c	Sat Mar 03 06:08:22 2018 -0500
+++ b/mercurial/cext/pathencode.c	Sat Mar 03 06:18:47 2018 -0500
@@ -512,7 +512,8 @@
 	Py_ssize_t len, newlen;
 	PyObject *ret;
 
-	if (!PyArg_ParseTuple(args, "s#:lowerencode", &path, &len))
+	if (!PyArg_ParseTuple(args, PY23("s#:lowerencode", "y#:lowerencode"),
+	                      &path, &len))
 		return NULL;
 
 	newlen = _lowerencode(NULL, 0, path, len);