diff --git a/src/Network/WebSockets/Simple.hs b/src/Network/WebSockets/Simple.hs
--- a/src/Network/WebSockets/Simple.hs
+++ b/src/Network/WebSockets/Simple.hs
@@ -10,10 +10,11 @@
 
 module Network.WebSockets.Simple
   ( -- * Types
-    WebSocketsApp (..), WebSocketsAppParams (..), WebSocketsAppThreads (..)
-  , Network.WebSockets.ConnectionException (..), WebSocketsSimpleError (..)
+    WebSocketsApp (..), WebSocketsAppParams (..)
+  , Network.WebSockets.ConnectionException (..), CloseOrigin (..), WebSocketsSimpleError (..)
   , -- * Running
-    toClientAppT, toClientAppT', toServerAppT
+    toClientAppT
+  , toServerAppT
   , -- * Utilities
     expBackoffStrategy
   , hoistWebSocketsApp
@@ -26,12 +27,11 @@
 import qualified Data.Aeson as Aeson
 import Data.ByteString.Lazy (ByteString)
 
-import Control.Monad (void, forever)
+import Control.Monad (forever)
 import Control.Monad.IO.Class (MonadIO (..))
 import Control.Monad.Catch (Exception, throwM, MonadThrow, catch, MonadCatch)
 import Control.Monad.Trans.Control (MonadBaseControl (..))
 import Control.Concurrent (threadDelay)
-import Control.Concurrent.Async (Async, async, link)
 import Control.Concurrent.STM (atomically, newTVarIO, readTVarIO, writeTVar)
 
 import GHC.Generics (Generic)
@@ -48,15 +48,21 @@
 data WebSocketsApp m receive send = WebSocketsApp
   { onOpen    :: WebSocketsAppParams m send -> m ()
   , onReceive :: WebSocketsAppParams m send -> receive -> m ()
-  , onClose   :: ConnectionException -> m () -- ^ Should be re-entrant; this exception is caught in all uses of 'send', even if used in a dead 'Network.WebSockets.Connection' in a lingering thread.
+  , onClose   :: CloseOrigin -> ConnectionException -> m () -- ^ Should be re-entrant; this exception is caught in all uses of 'send', even if used in a dead 'Network.WebSockets.Connection' in a lingering thread.
   } deriving (Generic, Typeable)
 
+data CloseOrigin
+  = ClosedOnSend
+  | ClosedOnClose
+  | ClosedOnReceive
+
+
 instance Profunctor (WebSocketsApp m) where
   dimap :: forall a b c d. (a -> b) -> (c -> d) -> WebSocketsApp m b c -> WebSocketsApp m a d
   dimap receiveF sendF WebSocketsApp{onOpen,onReceive,onClose} = WebSocketsApp
     { onOpen = \params -> onOpen (getParams params)
     , onReceive = \params r -> onReceive (getParams params) (receiveF r)
-    , onClose = onClose
+    , onClose = \o e -> onClose o e
     }
     where
       getParams :: WebSocketsAppParams m d -> WebSocketsAppParams m c
@@ -68,9 +74,9 @@
                    -> WebSocketsApp m receive send
                    -> WebSocketsApp n receive send
 hoistWebSocketsApp f coF WebSocketsApp{onOpen,onReceive,onClose} = WebSocketsApp
-  { onOpen = \WebSocketsAppParams{send,close} -> f $ onOpen WebSocketsAppParams{send = coF . send, close = coF close}
-  , onReceive = \WebSocketsAppParams{send,close} r -> f $ onReceive WebSocketsAppParams{send = coF . send, close = coF close} r
-  , onClose = f . onClose
+  { onOpen = \WebSocketsAppParams{send,close} -> f (onOpen WebSocketsAppParams{send = coF . send, close = coF close})
+  , onReceive = \WebSocketsAppParams{send,close} r -> f (onReceive WebSocketsAppParams{send = coF . send, close = coF close} r)
+  , onClose = \o e -> f (onClose o e)
   }
 
 
@@ -79,12 +85,12 @@
   mempty = WebSocketsApp
     { onOpen = \_ -> pure ()
     , onReceive = \_ _ -> pure ()
-    , onClose = \_ -> pure ()
+    , onClose = \_ _ -> pure ()
     }
   mappend x y = WebSocketsApp
     { onOpen = \params -> onOpen x params *> onOpen y params
     , onReceive = \params r -> onReceive x params r *> onReceive y params r
-    , onClose = \mE -> onClose x mE *> onClose y mE
+    , onClose = \o mE -> onClose x o mE *> onClose y o mE
     }
 
 
@@ -98,21 +104,21 @@
                 , MonadCatch m
                 )
              => WebSocketsApp m receive send
-             -> ClientAppT m WebSocketsAppThreads
+             -> ClientAppT m () -- WebSocketsAppThreads
 toClientAppT WebSocketsApp{onOpen,onReceive,onClose} conn = do
   let send :: send -> m ()
-      send x = liftIO (sendTextData conn (Aeson.encode x)) `catch` onClose
+      send x = liftIO (sendTextData conn (Aeson.encode x)) `catch` (onClose ClosedOnSend)
 
       close :: m ()
-      close = liftIO (sendClose conn (Aeson.encode "requesting close")) `catch` onClose
+      close = liftIO (sendClose conn (Aeson.encode "requesting close")) `catch` (onClose ClosedOnClose)
 
       params :: WebSocketsAppParams m send
       params = WebSocketsAppParams{send,close}
 
   onOpen params
 
-  receivingThread <- liftBaseWith $ \runInBase -> async $ forever $
-    let go' = do
+  liftBaseWith $ \runInBase ->
+    let go' = forever $ do
           data' <- receiveDataMessage conn
           let data'' = case data' of
                         Text xs _ -> xs
@@ -120,26 +126,10 @@
           case Aeson.decode data'' of
             Nothing -> throwM (JSONParseError data'')
             Just received -> runInBase (onReceive params received)
-    in  go' `catch` (runInBase . onClose)
-
-  liftIO (link receivingThread)
-
-  pure $ WebSocketsAppThreads
-    { wsAppReceivingThread = receivingThread
-    }
+    in  go' `catch` (\e -> () <$ (runInBase (onClose ClosedOnReceive e)))
 
 
 
-toClientAppT' :: ( ToJSON send
-                 , FromJSON receive
-                 , MonadIO m
-                 , MonadBaseControl IO m
-                 , MonadThrow m
-                 , MonadCatch m
-                 ) => WebSocketsApp m receive send -> ClientAppT m ()
-toClientAppT' wsApp conn = void (toClientAppT wsApp conn)
-
-
 toServerAppT :: ( ToJSON send
                 , FromJSON receive
                 , MonadIO m
@@ -147,9 +137,8 @@
                 , MonadThrow m
                 , MonadCatch m
                 ) => WebSocketsApp m receive send -> ServerAppT m
-toServerAppT wsApp pending = do
-  conn <- liftBaseWith $ \_ -> acceptRequest pending
-  toClientAppT' wsApp conn
+toServerAppT wsApp pending =
+  liftIO (acceptRequest pending) >>= toClientAppT wsApp
 
 
 
@@ -183,7 +172,3 @@
 
 instance Exception WebSocketsSimpleError
 
-
-newtype WebSocketsAppThreads = WebSocketsAppThreads
-  { wsAppReceivingThread :: Async ()
-  }
diff --git a/src/Test/WebSockets/Simple.hs b/src/Test/WebSockets/Simple.hs
--- a/src/Test/WebSockets/Simple.hs
+++ b/src/Test/WebSockets/Simple.hs
@@ -7,7 +7,7 @@
 
 module Test.WebSockets.Simple where
 
-import Network.WebSockets.Simple (WebSocketsApp (..), WebSocketsAppParams (..), ConnectionException (..))
+import Network.WebSockets.Simple (WebSocketsApp (..), WebSocketsAppParams (..), ConnectionException (..), CloseOrigin (..))
 import Control.Monad (forever, void)
 import Control.Monad.IO.Class (MonadIO (..))
 import Control.Monad.Trans.Control (MonadBaseControl (..))
@@ -36,8 +36,8 @@
 
       close :: m ()
       close = do
-        onClose sendsRreceivesS ConnectionClosed
-        onClose sendsSreceivesR ConnectionClosed
+        onClose sendsRreceivesS ClosedOnClose ConnectionClosed
+        onClose sendsSreceivesR ClosedOnClose ConnectionClosed
 
   sToR <- liftBaseWith $ \runInBase -> async $ forever $ do
     s <- atomically $ readTChan sendChan
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -23,7 +23,7 @@
       putStrLn "sent."
   , onReceive = \_ x ->
       atomically $ writeTChan receivedChan x
-  , onClose = \_ -> pure ()
+  , onClose = \_ _ -> pure ()
   }
 
 testSendingApp :: WebSocketsApp IO Int Int
@@ -34,7 +34,7 @@
       threadDelay $ 10^6 * 10
       send x
       putStrLn "sent."
-  , onClose = \_ -> pure ()
+  , onClose = \_ _ -> pure ()
   }
 
 
diff --git a/websockets-simple.cabal b/websockets-simple.cabal
--- a/websockets-simple.cabal
+++ b/websockets-simple.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 0fd7a69684c73e2d69f006be6b9f3028e804149928f115366bc6ef246ebe1cf5
+-- hash: d677af901275b84a23a53024bc83e2471998b8ed21dc32553b0a23c736723cd1
 
 name:           websockets-simple
-version:        0.0.7
+version:        0.1.0
 synopsis:       Composable websockets clients
 description:    See README at <https://github.com/athanclark/websockets-simple#readme>
 category:       Web
@@ -46,7 +46,7 @@
     , stm
     , transformers
     , wai-transformers
-    , websockets >=0.11
+    , websockets >=0.12.3
   default-language: Haskell2010
 
 test-suite spec
@@ -76,6 +76,6 @@
     , tasty-hspec
     , transformers
     , wai-transformers
-    , websockets >=0.11
+    , websockets >=0.12.3
     , websockets-simple
   default-language: Haskell2010