diff -r dbad4564cd12 Doc/library/concurrent.futures.rst
--- a/Doc/library/concurrent.futures.rst	Mon Jan 27 12:18:49 2014 +0100
+++ b/Doc/library/concurrent.futures.rst	Mon Jan 27 12:45:47 2014 -0500
@@ -338,7 +338,8 @@
 
    Wait for the :class:`Future` instances (possibly created by different
    :class:`Executor` instances) given by *fs* to complete.  Returns a named
-   2-tuple of sets.  The first set, named ``done``, contains the futures that
+   2-tuple of sets. Any futures given by *fs* that are duplicated will be 
+   returned once. The first set, named ``done``, contains the futures that
    completed (finished or were cancelled) before the wait completed.  The second
    set, named ``not_done``, contains uncompleted futures.
 
diff -r dbad4564cd12 Lib/concurrent/futures/_base.py
--- a/Lib/concurrent/futures/_base.py	Mon Jan 27 12:18:49 2014 +0100
+++ b/Lib/concurrent/futures/_base.py	Mon Jan 27 12:45:47 2014 -0500
@@ -251,12 +251,14 @@
         A named 2-tuple of sets. The first set, named 'done', contains the
         futures that completed (is finished or cancelled) before the wait
         completed. The second set, named 'not_done', contains uncompleted
-        futures.
+        futures. If any given Futures are duplicated, they will be returned 
+        once.
     """
+    fs = set(fs)
     with _AcquireFutures(fs):
         done = set(f for f in fs
                    if f._state in [CANCELLED_AND_NOTIFIED, FINISHED])
-        not_done = set(fs) - done
+        not_done = fs - done
 
         if (return_when == FIRST_COMPLETED) and done:
             return DoneAndNotDoneFutures(done, not_done)
diff -r dbad4564cd12 Lib/test/test_concurrent_futures.py
--- a/Lib/test/test_concurrent_futures.py	Mon Jan 27 12:18:49 2014 +0100
+++ b/Lib/test/test_concurrent_futures.py	Mon Jan 27 12:45:47 2014 -0500
@@ -290,6 +290,20 @@
                               future1]), finished)
         self.assertEqual(set([future2]), pending)
 
+    def test_duplicate_futures(self):
+        # Issue #20369: wait() on duplicate finished futures should not timeout 
+        future1 = self.executor.submit(mul, 6, 7)
+        time.sleep(1)
+        self.assertEqual(future1._state, FINISHED, "Precondition not valid for test")
+        start = time.time()
+        done, notdone = futures.wait([future1,future1], 
+            return_when=futures.ALL_COMPLETED,
+            timeout=2)
+        end = time.time()
+        self.assertEqual( set([future1]), done)
+        self.assertEqual( len(notdone), 0)
+        self.assertLess(end-start, 2, "Wait timed out on finished duplicated futures")
+
 
 class ThreadPoolWaitTests(ThreadPoolMixin, WaitTests, unittest.TestCase):