diff -r c3970be8deca -r 2f47703c5489 mercurial/context.py
--- a/mercurial/context.py	Sat Oct 13 09:45:49 2018 -0400
+++ b/mercurial/context.py	Sat Oct 13 08:54:31 2018 -0400
@@ -2433,5 +2433,5 @@
 
     def write(self, data, flags, **kwargs):
         assert not flags
-        with open(self._path, "w") as f:
+        with open(self._path, "wb") as f:
             f.write(data)