diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,10 @@
 # ChangeLog for time-manager
 
+## 0.1.2
+
+* Holding `Weak ThreadId` to prevent thread leak again
+  [#1013](https://github.com/yesodweb/wai/pull/1013)
+
 ## 0.1.1
 
 * Removing `unliftio`.
diff --git a/System/TimeManager.hs b/System/TimeManager.hs
--- a/System/TimeManager.hs
+++ b/System/TimeManager.hs
@@ -28,12 +28,13 @@
     TimeoutThread (..),
 ) where
 
-import Control.Concurrent (myThreadId)
+import Control.Concurrent (myThreadId, mkWeakThreadId)
 import qualified Control.Exception as E
 import Control.Reaper
 import Data.IORef (IORef)
 import qualified Data.IORef as I
 import Data.Typeable (Typeable)
+import GHC.Weak (deRefWeak)
 
 ----------------------------------------------------------------
 
@@ -107,14 +108,14 @@
 -- | Registering a timeout action of killing this thread.
 registerKillThread :: Manager -> TimeoutAction -> IO Handle
 registerKillThread m onTimeout = do
-    -- If we hold ThreadId, the stack and data of the thread is leaked.
-    -- If we hold Weak ThreadId, the stack is released. However, its
-    -- data is still leaked probably because of a bug of GHC.
-    -- So, let's just use ThreadId and release ThreadId by
-    -- overriding the timeout action by "cancel".
     tid <- myThreadId
+    wtid <- mkWeakThreadId tid
     -- First run the timeout action in case the child thread is masked.
-    register m $ onTimeout `E.finally` E.throwTo tid TimeoutThread
+    register m $ onTimeout `E.finally` do
+        mtid <- deRefWeak wtid
+        case mtid of
+          Nothing -> return ()
+          Just tid' -> E.throwTo tid' TimeoutThread
 
 data TimeoutThread = TimeoutThread
     deriving (Typeable)
diff --git a/time-manager.cabal b/time-manager.cabal
--- a/time-manager.cabal
+++ b/time-manager.cabal
@@ -1,5 +1,5 @@
 Name:                time-manager
-Version:             0.1.1
+Version:             0.1.2
 Synopsis:            Scalable timer
 License:             MIT
 License-file:        LICENSE