diff -r c1a7ba57b4ff Lib/asyncio/futures.py
--- a/Lib/asyncio/futures.py	Thu Dec 12 23:07:40 2013 +0100
+++ b/Lib/asyncio/futures.py	Fri Dec 13 01:12:15 2013 +0100
@@ -7,6 +7,7 @@
 
 import concurrent.futures._base
 import logging
+import sys
 import traceback
 
 from . import events
@@ -17,6 +18,8 @@ from .log import logger
 _CANCELLED = 'CANCELLED'
 _FINISHED = 'FINISHED'
 
+PY34 = sys.version_info >= (3, 4)
+
 # TODO: Do we really want to depend on concurrent.futures internals?
 Error = concurrent.futures._base.Error
 CancelledError = concurrent.futures.CancelledError
@@ -162,6 +165,12 @@ class Future:
             res += '<{}>'.format(self._state)
         return res
 
+    if PY34:
+        def __del__(self):
+            if self._tb_logger is not None:
+                logger.error('Future/Task exception was never retrieved:\n%s',
+                             ''.join(self._tb_logger))
+
     def cancel(self):
         """Cancel the future and schedule callbacks.
 
@@ -214,9 +223,9 @@ class Future:
             raise CancelledError
         if self._state != _FINISHED:
             raise InvalidStateError('Result is not ready.')
-        if self._tb_logger is not None:
+        if not PY34 and self._tb_logger is not None:
             self._tb_logger.clear()
-            self._tb_logger = None
+        self._tb_logger = None
         if self._exception is not None:
             raise self._exception
         return self._result
@@ -233,9 +242,9 @@ class Future:
             raise CancelledError
         if self._state != _FINISHED:
             raise InvalidStateError('Exception is not set.')
-        if self._tb_logger is not None:
+        if not PY34 and self._tb_logger is not None:
             self._tb_logger.clear()
-            self._tb_logger = None
+        self._tb_logger = None
         return self._exception
 
     def add_done_callback(self, fn):
@@ -286,12 +295,17 @@ class Future:
         if self._state != _PENDING:
             raise InvalidStateError('{}: {!r}'.format(self._state, self))
         self._exception = exception
-        self._tb_logger = _TracebackLogger(exception)
         self._state = _FINISHED
         self._schedule_callbacks()
-        # Arrange for the logger to be activated after all callbacks
-        # have had a chance to call result() or exception().
-        self._loop.call_soon(self._tb_logger.activate)
+        if PY34:
+            self._tb_logger = traceback.format_exception(exception.__class__,
+                                                         exception,
+                                                         exception.__traceback__)
+        else:
+            self._tb_logger = _TracebackLogger(exception)
+            # Arrange for the logger to be activated after all callbacks
+            # have had a chance to call result() or exception().
+            self._loop.call_soon(self._tb_logger.activate)
 
     # Truly internal methods.