diff -r c093cc6e6c99 -r 313e3a279828 mercurial/pure/osutil.py
--- a/mercurial/pure/osutil.py	Thu Nov 07 03:59:22 2019 -0800
+++ b/mercurial/pure/osutil.py	Thu Nov 07 13:18:19 2019 -0500
@@ -257,7 +257,7 @@
                 creation = _OPEN_ALWAYS
                 flags |= _O_APPEND
             else:
-                raise ValueError(r"invalid mode: %s" % pycompat.sysstr(mode))
+                raise ValueError("invalid mode: %s" % pycompat.sysstr(mode))
 
             fh = _kernel32.CreateFileA(
                 name,