--- a/mercurial/debugcommands.py	Sat Mar 10 15:50:09 2018 +0900
+++ b/mercurial/debugcommands.py	Sat Mar 10 15:57:16 2018 +0900
@@ -1119,7 +1119,7 @@
 
     def writetemp(contents):
         (fd, name) = tempfile.mkstemp(prefix="hg-debuginstall-")
-        f = os.fdopen(fd, pycompat.sysstr("wb"))
+        f = os.fdopen(fd, r"wb")
         f.write(contents)
         f.close()
         return name