diff --git a/mitmproxy/addonmanager.py b/mitmproxy/addonmanager.py
index 70cfda309..37c501ee2 100644
--- a/mitmproxy/addonmanager.py
+++ b/mitmproxy/addonmanager.py
@@ -230,7 +230,7 @@ class AddonManager:
 
         self.trigger(name, message)
 
-        if message.reply.state != "taken":
+        if message.reply.state == "start":
             message.reply.take()
             if not message.reply.has_message:
                 message.reply.ack()
diff --git a/mitmproxy/controller.py b/mitmproxy/controller.py
index 63117ef03..f39c1b24f 100644
--- a/mitmproxy/controller.py
+++ b/mitmproxy/controller.py
@@ -105,16 +105,16 @@ class Reply:
         self.q.put(self.value)
 
     def ack(self, force=False):
-        if self.state not in {"start", "taken"}:
-            raise exceptions.ControlException(
-                "Reply is {}, but expected it to be start or taken.".format(self.state)
-            )
         self.send(self.obj, force)
 
     def kill(self, force=False):
         self.send(exceptions.Kill, force)
 
     def send(self, msg, force=False):
+        if self.state not in {"start", "taken"}:
+            raise exceptions.ControlException(
+                "Reply is {}, but expected it to be start or taken.".format(self.state)
+            )
         if self.has_message and not force:
             raise exceptions.ControlException("There is already a reply message.")
         self.value = msg
diff --git a/mitmproxy/flow.py b/mitmproxy/flow.py
index 111566b8d..944c032d8 100644
--- a/mitmproxy/flow.py
+++ b/mitmproxy/flow.py
@@ -1,13 +1,12 @@
 import time
+import typing  # noqa
 import uuid
 
-from mitmproxy import controller  # noqa
-from mitmproxy import stateobject
 from mitmproxy import connections
+from mitmproxy import controller, exceptions  # noqa
+from mitmproxy import stateobject
 from mitmproxy import version
 
-import typing  # noqa
-
 
 class Error(stateobject.StateObject):
 
@@ -145,7 +144,11 @@ class Flow(stateobject.StateObject):
 
     @property
     def killable(self):
-        return self.reply and self.reply.state == "taken"
+        return (
+            self.reply and
+            self.reply.state in {"start", "taken"} and
+            self.reply.value != exceptions.Kill
+        )
 
     def kill(self):
         """
@@ -153,13 +156,7 @@ class Flow(stateobject.StateObject):
         """
         self.error = Error("Connection killed")
         self.intercepted = False
-
-        # reply.state should be "taken" here, or .take() will raise an
-        # exception.
-        if self.reply.state != "taken":
-            self.reply.take()
         self.reply.kill(force=True)
-        self.reply.commit()
         self.live = False
 
     def intercept(self):
diff --git a/test/mitmproxy/proxy/protocol/test_websocket.py b/test/mitmproxy/proxy/protocol/test_websocket.py
index a7acdc4db..d9389faf8 100644
--- a/test/mitmproxy/proxy/protocol/test_websocket.py
+++ b/test/mitmproxy/proxy/protocol/test_websocket.py
@@ -221,6 +221,25 @@ class TestSimple(_WebSocketTest):
         assert frame.payload == b'foo'
 
 
+class TestKillFlow(_WebSocketTest):
+
+    @classmethod
+    def handle_websockets(cls, rfile, wfile):
+        wfile.write(bytes(websockets.Frame(fin=1, opcode=websockets.OPCODE.TEXT, payload=b'server-foobar')))
+        wfile.flush()
+
+    def test_kill(self):
+        class KillFlow:
+            def websocket_message(self, f):
+                f.kill()
+
+        self.master.addons.add(KillFlow())
+        self.setup_connection()
+
+        with pytest.raises(exceptions.TcpDisconnect):
+            websockets.Frame.from_file(self.client.rfile)
+
+
 class TestSimpleTLS(_WebSocketTest):
     ssl = True