diff -r 418ab34fd1ce Lib/test/test_thread.py
--- a/Lib/test/test_thread.py	Sat May 30 00:53:26 2015 +0300
+++ b/Lib/test/test_thread.py	Fri May 29 16:01:42 2015 -0700
@@ -241,6 +241,62 @@
         self.assertEqual(os.read(self.read_fd, 2), "OK",
                          "Unable to fork() in thread")
 
+    @unittest.skipIf(sys.platform.startswith('win'),
+                     "This test is only appropriate for POSIX-like systems.")
+    @test_support.reap_threads
+    def test_replacement_threads_in_child(self):
+        """Test that sys._current_frames is aware of threads started in the child."""
+
+        stop = False
+
+        started_t1 = []
+        started_t2 = []
+
+        def do_nothing():
+            started_t1
+            started_t1.append(True)
+            while not stop:
+                pass
+
+        def do_nothing2():
+            started_t2.append(True)
+            while not stop:
+                pass
+
+        # Before the fork, we start do_nothing. In the child, we start do_nothing2.
+        # it should be the case that, in the child, the frame for do_nothing2 shows
+        # up in sys._current_frames()
+        try:
+            t1 = thread.start_new_thread(do_nothing, ())
+            while not started_t1:
+                time.sleep(.1)
+            r_fd, w_fd = os.pipe()
+            pid = os.fork()
+            if pid == 0:  # child
+                try:
+                    os.close(r_fd)
+                    t2 = thread.start_new_thread(do_nothing2, ())
+                    while not started_t2:
+                        time.sleep(.1)
+                    running_names = [
+                        frame.f_code.co_name for frame in sys._current_frames().values()]
+                    with os.fdopen(w_fd, 'w') as f:
+                        f.write(' '.join(name for name in running_names
+                                         if name != 'test_replacement_threads_in_child'))
+                except:
+                    traceback.print_exc()
+                    os._exit(1)
+                finally:
+                    os._exit(0)
+            else:  # parent
+                os.close(w_fd)
+                with os.fdopen(r_fd) as f:
+                    running_thread = f.read()
+                self.assertEqual(0, os.waitpid(pid, 0)[1])
+                self.assertEqual(running_thread, 'do_nothing2')
+        finally:
+            stop = True
+
     def tearDown(self):
         try:
             os.close(self.read_fd)
diff -r 418ab34fd1ce Python/pystate.c
--- a/Python/pystate.c	Sat May 30 00:53:26 2015 +0300
+++ b/Python/pystate.c	Fri May 29 16:01:42 2015 -0700
@@ -480,7 +480,9 @@
             id = PyInt_FromLong(t->thread_id);
             if (id == NULL)
                 goto Fail;
-            stat = PyDict_SetItem(result, id, (PyObject *)frame);
+            stat = PyDict_Contains(result, id);
+            if (stat == 0)
+                stat = PyDict_SetItem(result, id, (PyObject *)frame);
             Py_DECREF(id);
             if (stat < 0)
                 goto Fail;