diff --git a/mercurial/cext/pathencode.c b/mercurial/cext/pathencode.c
--- a/mercurial/cext/pathencode.c
+++ b/mercurial/cext/pathencode.c
@@ -678,7 +678,7 @@
 		}
 	}
 
-	shaobj = PyObject_CallFunction(shafunc, "s#", str, len);
+	shaobj = PyObject_CallFunction(shafunc, PY23("s#", "y#"), str, len);
 
 	if (shaobj == NULL)
 		return -1;