diff --git a/Lib/multiprocessing/__init__.py b/Lib/multiprocessing/__init__.py
--- a/Lib/multiprocessing/__init__.py
+++ b/Lib/multiprocessing/__init__.py
@@ -114,7 +114,13 @@
             num = int(os.environ['NUMBER_OF_PROCESSORS'])
         except (ValueError, KeyError):
             num = 0
-    elif 'bsd' in sys.platform or sys.platform == 'darwin':
+    elif sys.platform == 'darwin':
+        try:
+            with os.popen('/usr/sbin/sysctl -n hw.ncpu') as p:
+                num = int(p.read())
+        except ValueError:
+            num = 0
+    elif 'bsd' in sys.platform:
         try:
             with os.popen('sysctl -n hw.ncpu') as p:
                 num = int(p.read())