diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
--- a/mercurial/pycompat.py
+++ b/mercurial/pycompat.py
@@ -314,3 +314,5 @@
     stringio = cStringIO.StringIO
     maplist = map
     rawinput = raw_input
+
+isjython = sysplatform.startswith('java')
diff --git a/mercurial/selectors2.py b/mercurial/selectors2.py
--- a/mercurial/selectors2.py
+++ b/mercurial/selectors2.py
@@ -29,12 +29,13 @@
 import collections
 import errno
 import math
-import platform
 import select
 import socket
 import sys
 import time
 
+from . import pycompat
+
 namedtuple = collections.namedtuple
 Mapping = collections.Mapping
 
@@ -288,7 +289,7 @@
     __all__.append('SelectSelector')
 
     # Jython has a different implementation of .fileno() for socket objects.
-    if platform.system() == 'Java':
+    if pycompat.isjython:
         class _JythonSelectorMapping(object):
             """ This is an implementation of _SelectorMapping that is built
             for use specifically with Jython, which does not provide a hashable
@@ -727,7 +728,7 @@
     by eventlet, greenlet, and preserve proper behavior. """
     global _DEFAULT_SELECTOR
     if _DEFAULT_SELECTOR is None:
-        if platform.system() == 'Java':  # Platform-specific: Jython
+        if pycompat.isjython:
             _DEFAULT_SELECTOR = JythonSelectSelector
         elif _can_allocate('kqueue'):
             _DEFAULT_SELECTOR = KqueueSelector