--- a/mercurial/util.py	Thu Oct 12 23:30:46 2017 -0700
+++ b/mercurial/util.py	Thu Oct 12 09:04:22 2017 -0700
@@ -313,7 +313,7 @@
             return memoryview(sliceable)[offset:offset + length]
         return memoryview(sliceable)[offset:]
 
-closefds = pycompat.osname == 'posix'
+closefds = pycompat.isposix
 
 _chunksize = 4096