diff -r 5d41ebc79738 Lib/test/test_threading.py
--- a/Lib/test/test_threading.py	Sun Jul 07 09:49:23 2013 +0200
+++ b/Lib/test/test_threading.py	Tue Jul 09 18:12:26 2013 -0400
@@ -443,6 +443,20 @@
         self.assertEqual(out, '')
         self.assertEqual(err, '')
 
+    @unittest.skipUnless(hasattr(os, 'fork'), "needs os.fork()")
+    def test_is_alive_after_fork(self):
+        # Issue #0: is_alive() could sometimes be True on threads that vanished
+        # after a fork.
+
+        t = threading.Thread(target=lambda: None)
+        t.start()
+        pid = os.fork()
+        if pid == 0:
+            os._exit(1 if t.is_alive() else 0)
+        else:
+            (_, exit_status) = os.waitpid(pid, 0)
+            self.assertEqual(0, exit_status)
+
 
 class ThreadJoinOnShutdown(BaseTestCase):
 
diff -r 5d41ebc79738 Lib/threading.py
--- a/Lib/threading.py	Sun Jul 07 09:49:23 2013 +0200
+++ b/Lib/threading.py	Tue Jul 09 18:12:26 2013 -0400
@@ -790,10 +790,10 @@
     def __bootstrap_inner(self):
         try:
             self._set_ident()
-            self.__started.set()
             with _active_limbo_lock:
                 _active[self.__ident] = self
                 del _limbo[self]
+            self.__started.set()
             if __debug__:
                 self._note("%s.__bootstrap(): thread started", self)