diff --git a/mitogen/parent.py b/mitogen/parent.py
index 089d8603..692adf24 100644
--- a/mitogen/parent.py
+++ b/mitogen/parent.py
@@ -422,8 +422,41 @@ def discard_until(fd, s, deadline):
             return
 
 
+def _upgrade_broker(broker):
+    """
+    Extract the poller state from Broker and replace it with the industrial
+    strength poller for this OS. Must run on the Broker thread.
+    """
+    # This function is deadly! The act of calling start_receive() generates log
+    # messages which must be silenced as the upgrade progresses, otherwise the
+    # poller state will change as it is copied, resulting in write fds that are
+    # lost. (Due to LogHandler->Router->Stream->Broker->Poller, where Stream
+    # only calls start_transmit() when transitioning from empty to non-empty
+    # buffer. If the start_transmit() is lost, writes from the child hang
+    # permanently).
+    root = logging.getLogger()
+    old_level = root.level
+    root.setLevel(logging.CRITICAL)
+
+    old = broker.poller
+    new = PREFERRED_POLLER()
+    for fd, data in old.readers:
+        new.start_receive(fd, data)
+    for fd, data in old.writers:
+        new.start_transmit(fd, data)
+
+    old.close()
+    broker.poller = new
+    root.setLevel(old_level)
+    LOG.debug('replaced %r with %r (new: %d readers, %d writers; '
+              'old: %d readers, %d writers)', old, new,
+              len(new.readers), len(new.writers),
+              len(old.readers), len(old.writers))
+
+
 def upgrade_router(econtext):
     if not isinstance(econtext.router, Router):  # TODO
+        econtext.broker.defer(_upgrade_broker, econtext.broker)
         econtext.router.__class__ = Router  # TODO
         econtext.router.upgrade(
             importer=econtext.importer,
@@ -500,17 +533,7 @@ class Argv(object):
         return ' '.join(map(self.escape, self.argv))
 
 
-class Poller(mitogen.core.Poller):
-    @classmethod
-    def from_existing(cls, poller):
-        self = cls()
-        for fd, data in poller.readers:
-            self.start_receive(fd, data)
-        for fd, data in poller.writers:
-            self.start_transmit(fd, data)
-
-
-class KqueuePoller(Poller):
+class KqueuePoller(mitogen.core.Poller):
     _repr = 'KqueuePoller()'
 
     def __init__(self):
@@ -577,11 +600,11 @@ class KqueuePoller(Poller):
                 yield self._wfds[fd]
 
 
-class EpollPoller(Poller):
+class EpollPoller(mitogen.core.Poller):
     _repr = 'EpollPoller()'
 
     def __init__(self):
-        self._epoll = select.epoll()
+        self._epoll = select.epoll(32)
         self._registered_fds = set()
         self._rfds = {}
         self._wfds = {}
@@ -641,7 +664,7 @@ class EpollPoller(Poller):
         if timeout is not None:
             the_timeout = timeout
 
-        events, _ = mitogen.core.io_op(self._epoll.poll, the_timeout)
+        events, _ = mitogen.core.io_op(self._epoll.poll, the_timeout, 32)
         for fd, event in events:
             if event & self._inmask and fd in self._rfds:
                 # Events can still be read for an already-discarded fd.