diff -r edf736c3c064 -r f5427483eebe mercurial/util.py
--- a/mercurial/util.py	Fri Mar 02 13:47:49 2018 -0500
+++ b/mercurial/util.py	Fri Mar 02 14:09:20 2018 -0500
@@ -509,8 +509,8 @@
     )
 
     def __init__(self, fh, observer):
-        object.__setattr__(self, '_orig', fh)
-        object.__setattr__(self, '_observer', observer)
+        object.__setattr__(self, r'_orig', fh)
+        object.__setattr__(self, r'_observer', observer)
 
     def __getattribute__(self, name):
         ours = {