diff --git a/CHANGELOG b/CHANGELOG
index 4bd4f0e9e6..f2e4b19509 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,10 @@
+git-annex (8.20201128) UNRELEASED; urgency=medium
+
+  * Fix hang on shutdown of external special remote using ASYNC protocol
+    extension. (Reversion introduced in version 8.20201007.)
+
+ -- Joey Hess <id@joeyh.name>  Mon, 30 Nov 2020 12:55:49 -0400
+
 git-annex (8.20201127) upstream; urgency=medium
 
   * adjust: New --unlock-present mode which locks files whose content is not
diff --git a/Remote/External/AsyncExtension.hs b/Remote/External/AsyncExtension.hs
index e0fdf9de4c..ee60bc8e2f 100644
--- a/Remote/External/AsyncExtension.hs
+++ b/Remote/External/AsyncExtension.hs
@@ -28,8 +28,8 @@ runRelayToExternalAsync external st = do
 	jidmap <- newTVarIO M.empty
 	sendq <- newSendQueue
 	nextjid <- newTVarIO (JobId 1)
-	void $ async $ sendloop st sendq
-	void $ async $ receiveloop external st jidmap sendq
+	sender <- async $ sendloop st sendq
+	receiver <- async $ receiveloop external st jidmap sendq sender
 	return $ ExternalAsyncRelay $ do
 		receiveq <- newReceiveQueue
 		jid <- atomically $ do
@@ -44,7 +44,7 @@ runRelayToExternalAsync external st = do
 					(toAsyncWrapped msg, jid)
 			, externalReceive = atomically (readTBMChan receiveq)
 			-- This shuts down the whole relay.
-			, externalShutdown = shutdown external st sendq
+			, externalShutdown = shutdown external st sendq sender receiver
 			-- These three TMVars are shared amoung all
 			-- ExternalStates that use this relay; they're
 			-- common state about the external process.
@@ -65,14 +65,14 @@ newReceiveQueue = newTBMChanIO 10
 newSendQueue :: IO SendQueue
 newSendQueue = newTBMChanIO 10
 
-receiveloop :: External -> ExternalState -> JidMap -> SendQueue -> IO ()
-receiveloop external st jidmap sendq = externalReceive st >>= \case
+receiveloop :: External -> ExternalState -> JidMap -> SendQueue -> Async () -> IO ()
+receiveloop external st jidmap sendq sendthread = externalReceive st >>= \case
 	Just l -> case parseMessage l :: Maybe AsyncMessage of
 		Just (AsyncMessage jid msg) ->
 			M.lookup jid <$> readTVarIO jidmap >>= \case
 				Just c -> do
 					atomically $ writeTBMChan c msg
-					receiveloop external st jidmap sendq
+					receiveloop external st jidmap sendq sendthread
 				Nothing -> protoerr "unknown job number"
 		Nothing -> case parseMessage l :: Maybe ExceptionalMessage of
 			Just _ -> do
@@ -80,7 +80,7 @@ receiveloop external st jidmap sendq = externalReceive st >>= \case
 				m <- readTVarIO jidmap
 				forM_ (M.elems m) $ \c ->
 					atomically  $ writeTBMChan c l
-				receiveloop external st jidmap sendq
+				receiveloop external st jidmap sendq sendthread
 			Nothing -> protoerr "unexpected non-async message"
 	Nothing -> closeandshutdown
   where
@@ -89,7 +89,8 @@ receiveloop external st jidmap sendq = externalReceive st >>= \case
 		closeandshutdown
 	
 	closeandshutdown = do
-		shutdown external st sendq True
+		dummy <- async noop
+		shutdown external st sendq sendthread dummy True
 		m <- atomically $ readTVar jidmap
 		forM_ (M.elems m) (atomically . closeTBMChan)
 
@@ -110,8 +111,15 @@ sendloop st sendq = atomically (readTBMChan sendq) >>= \case
   where
 	wrapjid msg jid = AsyncMessage jid $ unwords $ Proto.formatMessage msg
 
-shutdown :: External -> ExternalState -> SendQueue -> Bool -> IO ()
-shutdown external st sendq b = do
+shutdown :: External -> ExternalState -> SendQueue -> Async () -> Async () -> Bool -> IO ()
+shutdown external st sendq sendthread receivethread b = do
+	-- Receive thread is normally blocked reading from a handle.
+	-- That can block closing the handle, so it needs to be canceled.
+	cancel receivethread
+	-- Cleanly shutdown the send thread as well, allowing it to finish
+	-- writing anything that was buffered.
+	atomically $ closeTBMChan sendq
+	wait sendthread
 	r <- atomically $ do
 		r <- tryTakeTMVar (externalAsync external) 
 		putTMVar (externalAsync external)
@@ -120,4 +128,3 @@ shutdown external st sendq b = do
 	case r of
 		Just (ExternalAsync _) -> externalShutdown st b
 		_ -> noop
-	atomically $ closeTBMChan sendq
diff --git a/doc/bugs/async_external_special_remote__39__s_stdin_not_closed.mdwn b/doc/bugs/async_external_special_remote__39__s_stdin_not_closed.mdwn
index 5551dee897..a4e7059be9 100644
--- a/doc/bugs/async_external_special_remote__39__s_stdin_not_closed.mdwn
+++ b/doc/bugs/async_external_special_remote__39__s_stdin_not_closed.mdwn
@@ -167,3 +167,5 @@ everything under control for the first time; I'm not all the way there yet, but
 I finally have an idea of how to handle it all. I started developing something
 to do the file management myself, but embraced git-annex wholeheartedly once I
 grokked it.
+
+> [[fixed|done]] --[[Joey]]