diff --git a/maint/vm/ubuntu12.04/tox.ini b/maint/vm/ubuntu12.04/tox.ini
index fdf6f1f9..a7772091 100644
--- a/maint/vm/ubuntu12.04/tox.ini
+++ b/maint/vm/ubuntu12.04/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py27-full, py25-full, py32, py25, py27, py27-select
+envlist = py27-full, py25-full, py32, py25, py27, py27-select, py27-twisted
 setupdir=/tornado
 toxworkdir=/home/vagrant/tox-tornado
 
@@ -36,3 +36,11 @@ deps =
      pycurl
      twisted==12.2.0
 commands = python -m tornado.test.runtests --ioloop=tornado.platform.select.SelectIOLoop {posargs:}
+
+[testenv:py27-twisted]
+basepython = python2.7
+deps =
+     futures
+     pycurl
+     twisted==12.2.0
+commands = python -m tornado.test.runtests --ioloop=tornado.platform.twisted.TwistedIOLoop {posargs:}
diff --git a/tornado/platform/twisted.py b/tornado/platform/twisted.py
index ff43e633..6c3cbf96 100644
--- a/tornado/platform/twisted.py
+++ b/tornado/platform/twisted.py
@@ -191,6 +191,8 @@ class TornadoReactor(PosixReactorBase):
 
     # IReactorFDSet
     def _invoke_callback(self, fd, events):
+        if fd not in self._fds:
+            return
         (reader, writer) = self._fds[fd]
         if reader:
             err = None
@@ -356,18 +358,23 @@ class _FD(object):
         self.handler = handler
         self.reading = False
         self.writing = False
+        self.lost = False
 
     def fileno(self):
         return self.fd
 
     def doRead(self):
-        self.handler(self.fd, tornado.ioloop.IOLoop.READ)
+        if not self.lost:
+            self.handler(self.fd, tornado.ioloop.IOLoop.READ)
 
     def doWrite(self):
-        self.handler(self.fd, tornado.ioloop.IOLoop.WRITE)
+        if not self.lost:
+            self.handler(self.fd, tornado.ioloop.IOLoop.WRITE)
 
     def connectionLost(self, reason):
-        self.handler(self.fd, tornado.ioloop.IOLoop.ERROR)
+        if not self.lost:
+            self.handler(self.fd, tornado.ioloop.IOLoop.ERROR)
+            self.lost = True
 
     def logPrefix(self):
         return ''
@@ -424,6 +431,7 @@ class TwistedIOLoop(tornado.ioloop.IOLoop):
                 self.reactor.removeWriter(self.fds[fd])
 
     def remove_handler(self, fd):
+        self.fds[fd].lost = True
         if self.fds[fd].reading:
             self.reactor.removeReader(self.fds[fd])
         if self.fds[fd].writing:
diff --git a/tornado/test/httpclient_test.py b/tornado/test/httpclient_test.py
index 54ebc749..d3e9e551 100644
--- a/tornado/test/httpclient_test.py
+++ b/tornado/test/httpclient_test.py
@@ -133,6 +133,7 @@ Transfer-Encoding: chunked
             resp = self.wait()
             resp.rethrow()
             self.assertEqual(resp.body, b("12"))
+            self.io_loop.remove_handler(sock.fileno())
 
     def test_basic_auth(self):
         self.assertEqual(self.fetch("/auth", auth_username="Aladdin",
diff --git a/tornado/test/ioloop_test.py b/tornado/test/ioloop_test.py
index 023c3a39..27c58bd3 100644
--- a/tornado/test/ioloop_test.py
+++ b/tornado/test/ioloop_test.py
@@ -62,6 +62,7 @@ class TestIOLoop(AsyncTestCase):
                               sock.fileno(), lambda fd, events: None,
                               IOLoop.READ)
         finally:
+            self.io_loop.remove_handler(sock.fileno())
             sock.close()
 
     def test_add_callback_from_signal(self):
diff --git a/tornado/test/process_test.py b/tornado/test/process_test.py
index edd7f2b4..43748ebc 100644
--- a/tornado/test/process_test.py
+++ b/tornado/test/process_test.py
@@ -18,6 +18,11 @@ from tornado.test.util import unittest, skipIfNonUnix
 from tornado.util import b
 from tornado.web import RequestHandler, Application
 
+
+def skip_if_twisted():
+    if IOLoop.configured_class().__name__ == 'TwistedIOLoop':
+        raise unittest.SkipTest("Process tests not compatible with TwistedIOLoop")
+
 # Not using AsyncHTTPTestCase because we need control over the IOLoop.
 class ProcessTest(unittest.TestCase):
     def get_app(self):
@@ -49,6 +54,9 @@ class ProcessTest(unittest.TestCase):
         super(ProcessTest, self).tearDown()
 
     def test_multi_process(self):
+        # This test can't work on twisted because we use the global reactor
+        # and have no way to get it back into a sane state after the fork.
+        skip_if_twisted()
         with ExpectLog(gen_log, "(Starting .* processes|child .* exited|uncaught exception)"):
             self.assertFalse(IOLoop.initialized())
             sock, port = bind_unused_port()
@@ -144,12 +152,9 @@ class SubprocessTest(AsyncTestCase):
         data = self.wait()
         self.assertEqual(data, b(""))
 
-    def skip_if_twisted(self):
-        if self.io_loop.__class__.__name__ == 'TwistedIOLoop':
-            raise unittest.SkipTest("SIGCHLD not compatible with Twisted IOLoop")
-
     def test_sigchild(self):
-        self.skip_if_twisted()
+        # Twisted's SIGCHLD handler and Subprocess's conflict with each other.
+        skip_if_twisted()
         Subprocess.initialize(io_loop=self.io_loop)
         self.addCleanup(Subprocess.uninitialize)
         subproc = Subprocess([sys.executable, '-c', 'pass'],
@@ -160,7 +165,7 @@ class SubprocessTest(AsyncTestCase):
         self.assertEqual(subproc.returncode, ret)
 
     def test_sigchild_signal(self):
-        self.skip_if_twisted()
+        skip_if_twisted()
         Subprocess.initialize(io_loop=self.io_loop)
         self.addCleanup(Subprocess.uninitialize)
         subproc = Subprocess([sys.executable, '-c',