diff -r 23746eb968f6 Lib/multiprocessing/pool.py
--- a/Lib/multiprocessing/pool.py	Tue Jul 07 12:21:03 2009 +0200
+++ b/Lib/multiprocessing/pool.py	Tue Jul 07 20:34:58 2009 +0900
@@ -209,6 +209,9 @@
             if extra:
                 chunksize += 1
 
+        if len(iterable) == 0:
+            chunksize = 0
+
         task_batches = Pool._get_tasks(func, iterable, chunksize)
         result = MapResult(self._cache, chunksize, len(iterable), callback)
         self._taskqueue.put((((result._job, i, mapstar, (x,), {})
diff -r 23746eb968f6 Lib/test/test_multiprocessing.py
--- a/Lib/test/test_multiprocessing.py	Tue Jul 07 12:21:03 2009 +0200
+++ b/Lib/test/test_multiprocessing.py	Tue Jul 07 20:34:58 2009 +0900
@@ -990,6 +990,12 @@
         self.assertEqual(pmap(sqr, list(range(100)), chunksize=20),
                          list(map(sqr, list(range(100)))))
 
+    def test_map_chunksize(self):
+        try:
+            self.pool.map_async(sqr, [], chunksize=1).get(timeout=TIMEOUT1)
+        except multiprocessing.TimeoutError:
+            self.fail("pool.map_async with chunksize stalled on null list")
+
     def test_async(self):
         res = self.pool.apply_async(sqr, (7, TIMEOUT1,))
         get = TimingWrapper(res.get)