--- a/mercurial/patch.py	Sun Feb 11 14:17:23 2018 -0800
+++ b/mercurial/patch.py	Sun Feb 11 14:18:27 2018 -0800
@@ -215,7 +215,7 @@
 
     data = {}
     fd, tmpname = tempfile.mkstemp(prefix='hg-patch-')
-    tmpfp = os.fdopen(fd, pycompat.sysstr('w'))
+    tmpfp = os.fdopen(fd, pycompat.sysstr('wb'))
     try:
         msg = pycompat.emailparser().parse(fileobj)