--- a/mercurial/patch.py	Fri Sep 15 00:01:57 2017 -0700
+++ b/mercurial/patch.py	Sun Sep 03 16:45:33 2017 +0900
@@ -46,9 +46,7 @@
 gitre = re.compile(br'diff --git a/(.*) b/(.*)')
 tabsplitter = re.compile(br'(\t+|[^\t]+)')
 
-class PatchError(Exception):
-    pass
-
+PatchError = error.PatchError
 
 # public functions