diff --git a/mercurial/worker.py b/mercurial/worker.py
--- a/mercurial/worker.py
+++ b/mercurial/worker.py
@@ -8,6 +8,7 @@
 from __future__ import absolute_import
 
 import errno
+import multiprocessing
 import os
 import signal
 import sys
@@ -18,24 +19,10 @@ from . import util
 
 def countcpus():
     '''try to count the number of CPUs on the system'''
-
-    # posix
     try:
-        n = int(os.sysconf('SC_NPROCESSORS_ONLN'))
-        if n > 0:
-            return n
-    except (AttributeError, ValueError):
-        pass
-
-    # windows
-    try:
-        n = int(os.environ['NUMBER_OF_PROCESSORS'])
-        if n > 0:
-            return n
-    except (KeyError, ValueError):
-        pass
-
-    return 1
+        return multiprocessing.cpu_count()
+    except NotImplementedError:
+        return 1
 
 def _numworkers(ui):
     s = ui.config('worker', 'numcpus')