diff --git a/mercurial/windows.py b/mercurial/windows.py
--- a/mercurial/windows.py
+++ b/mercurial/windows.py
@@ -70,7 +70,8 @@ class mixedfilemodewrapper(object):
         object.__setattr__(self, r'_lastop', 0)
 
     def __enter__(self):
-        return self._fp.__enter__()
+        self._fp.__enter__()
+        return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         self._fp.__exit__(exc_type, exc_val, exc_tb)