diff -r 232bf0028596 -r 83f6c4733ecc mercurial/windows.py
--- a/mercurial/windows.py	Tue Apr 07 22:30:25 2015 -0400
+++ b/mercurial/windows.py	Tue Apr 07 22:31:36 2015 -0400
@@ -363,7 +363,7 @@
     """Read all available data from a pipe."""
     chunks = []
     while True:
-        size = os.fstat(pipe.fileno()).st_size
+        size = win32.peekpipe(pipe)
         if not size:
             break