diff --git a/contrib/clang-format-ignorelist b/contrib/clang-format-ignorelist
--- a/contrib/clang-format-ignorelist
+++ b/contrib/clang-format-ignorelist
@@ -67,3 +67,4 @@
 mercurial/thirdparty/xdiff/xtypes.h
 mercurial/thirdparty/xdiff/xutils.c
 mercurial/thirdparty/xdiff/xutils.h
+mercurial/thirdparty/zope/interface/_zope_interface_coptimizations.c