diff --git a/docs/releases.rst b/docs/releases.rst
index 8de19077..3d067fe5 100644
--- a/docs/releases.rst
+++ b/docs/releases.rst
@@ -20,6 +20,7 @@ unreleased
 ----------
 
 `git master <https://github.com/meejah/txtorcon>`_ *will likely become v19.0.0*
+* add `TorControlProtocol.when_disconnected()` Returns a new deferred to each caller.
 
 v18.3.0
 -------
diff --git a/test/test_torcontrolprotocol.py b/test/test_torcontrolprotocol.py
index fe6d8e6f..8a0012f3 100644
--- a/test/test_torcontrolprotocol.py
+++ b/test/test_torcontrolprotocol.py
@@ -215,6 +215,38 @@ def it_was_called(*args):
         self.protocol.connectionLost(f)
         self.assertTrue(it_was_called.yes)
 
+    def test_when_disconnect(self):
+        """
+        see that we get our callback for when_disconnected if the
+        transport goes away
+        """
+        def it_was_called(arg):
+            it_was_called.yes = True
+            return None
+        it_was_called.yes = False
+
+        d = self.protocol.when_disconnected()
+        d.addCallback(it_was_called)
+        f = failure.Failure(error.ConnectionDone("It's all over"))
+        self.protocol.connectionLost(f)
+        self.assertTrue(it_was_called.yes)
+
+    def test_when_disconnect_error(self):
+        """
+        see that we get our errback for when_disconnected if the
+        transport goes away
+        """
+        def it_was_called(arg):
+            it_was_called.yes = True
+            return None
+        it_was_called.yes = False
+
+        d = self.protocol.when_disconnected()
+        d.addErrback(it_was_called)
+        f = failure.Failure(RuntimeError("sadness"))
+        self.protocol.connectionLost(f)
+        self.assertTrue(it_was_called.yes)
+
     def test_disconnect_errback(self):
         """
         see that we get our callback on_disconnect if the transport
diff --git a/txtorcon/torcontrolprotocol.py b/txtorcon/torcontrolprotocol.py
index db8ebf18..33421a57 100644
--- a/txtorcon/torcontrolprotocol.py
+++ b/txtorcon/torcontrolprotocol.py
@@ -23,7 +23,7 @@
 
 from txtorcon.interface import ITorControlProtocol
 from .spaghetti import FSM, State, Transition
-from .util import maybe_coroutine
+from .util import maybe_coroutine, SingleObserver
 
 
 DEFAULT_VALUE = 'DEFAULT'
@@ -271,6 +271,11 @@ def __init__(self, password_function=None):
         there was an error, the errback is called instead.
         """
 
+        self._when_disconnected = SingleObserver()
+        """
+        Private. See :func:`.when_disconnected`
+        """
+
         self.post_bootstrap = defer.Deferred()
         """
         This Deferred is triggered when we're done setting up
@@ -648,6 +653,13 @@ def queue_command(self, cmd, arg=None):
         self._maybe_issue_command()
         return d
 
+    def when_disconnected(self):
+        """
+        :returns: a Deferred that fires when (if) we disconnect from our
+            Tor process.
+        """
+        return self._when_disconnected.when_fired()
+
     # the remaining methods are internal API implementations,
     # callbacks and state-tracking methods -- you shouldn't have any
     # need to call them.
@@ -672,6 +684,11 @@ def connectionMade(self):
     def connectionLost(self, reason):
         "Protocol API"
         txtorlog.msg('connection terminated: ' + str(reason))
+        if reason.check(ConnectionDone):
+            self._when_disconnected.fire(self)
+        else:
+            self._when_disconnected.fire(reason)
+
         # ...and this is why we don't do on_disconnect = Deferred() :(
         # and instead should have had on_disconnect() method that
         # returned a new Deferred to each caller..(we're checking if