diff --git a/Network/Wai/Handler/Warp/Counter.hs b/Network/Wai/Handler/Warp/Counter.hs
--- a/Network/Wai/Handler/Warp/Counter.hs
+++ b/Network/Wai/Handler/Warp/Counter.hs
@@ -6,19 +6,19 @@
   , decrease
   ) where
 
-import Network.Wai.Handler.Warp.IORef
+import qualified Data.Atomics.Counter.Unboxed as C
 import Control.Applicative ((<$>))
 
-newtype Counter = Counter (IORef Int)
+newtype Counter = Counter C.AtomicCounter
 
 newCounter :: IO Counter
-newCounter = Counter <$> newIORef 0
+newCounter = Counter <$> C.newCounter 0
 
 isZero :: Counter -> IO Bool
-isZero (Counter ref) = (== 0) <$> readIORef ref
+isZero (Counter ref) = (== 0) <$> C.readCounter ref
 
 increase :: Counter -> IO ()
-increase (Counter ref) = atomicModifyIORef' ref $ \x -> (x + 1, ())
+increase (Counter ref) = C.incrCounter_ 1 ref
 
 decrease :: Counter -> IO ()
-decrease (Counter ref) = atomicModifyIORef' ref $ \x -> (x - 1, ())
+decrease (Counter ref) = C.incrCounter_ (-1) ref
diff --git a/Network/Wai/Handler/Warp/Timeout.hs b/Network/Wai/Handler/Warp/Timeout.hs
--- a/Network/Wai/Handler/Warp/Timeout.hs
+++ b/Network/Wai/Handler/Warp/Timeout.hs
@@ -56,11 +56,10 @@
 import Control.Concurrent (myThreadId)
 import qualified Control.Exception as E
 import GHC.Weak (Weak (..))
-import Network.Wai.Handler.Warp.IORef (IORef)
-import qualified Network.Wai.Handler.Warp.IORef as I
 import System.Mem.Weak (deRefWeak)
 import Data.Typeable (Typeable)
 import Control.Reaper
+import qualified Data.Atomics.Counter.Unboxed as C
 
 ----------------------------------------------------------------
 
@@ -71,12 +70,14 @@
 type TimeoutAction = IO ()
 
 -- | A handle used by 'Manager'
-data Handle = Handle TimeoutAction (IORef State)
+data Handle = Handle TimeoutAction {-# UNPACK #-} !C.AtomicCounter
 
-data State = Active    -- Manager turns it to Inactive.
-           | Inactive  -- Manager removes it with timeout action.
-           | Paused    -- Manager does not change it.
-           | Canceled  -- Manager removes it without timeout action.
+-- Four states for the AtomicCounter:
+--
+-- 1: Active    -- Manager turns it to Inactive.
+-- 2: Inactive  -- Manager removes it with timeout action.
+-- 3: Paused    -- Manager does not change it.
+-- 4: Canceled  -- Manager removes it without timeout action.
 
 ----------------------------------------------------------------
 
@@ -89,17 +90,15 @@
         }
   where
     prune m@(Handle onTimeout iactive) = do
-        state <- I.atomicModifyIORef' iactive (\x -> (inactivate x, x))
-        case state of
-            Inactive -> do
+        -- Try to change from active to inactive
+        (wasActive, newState) <- C.casCounter iactive 1 2
+        case newState of
+            2 | not wasActive -> do -- inactive
                 onTimeout `E.catch` ignoreAll
                 return Nothing
-            Canceled -> return Nothing
+            4 -> return Nothing -- canceled
             _        -> return $ Just m
 
-    inactivate Active = Inactive
-    inactivate x = x
-
 ----------------------------------------------------------------
 
 -- | Stopping timeout manager.
@@ -116,7 +115,7 @@
 -- | Registering a timeout action.
 register :: Manager -> TimeoutAction -> IO Handle
 register mgr onTimeout = do
-    iactive <- I.newIORef Active
+    iactive <- C.newCounter 1
     let h = Handle onTimeout iactive
     reaperAdd mgr h
     return h
@@ -153,17 +152,17 @@
 -- | Setting the state to active.
 --   'Manager' turns active to inactive repeatedly.
 tickle :: Handle -> IO ()
-tickle (Handle _ iactive) = I.writeIORef iactive Active
+tickle (Handle _ iactive) = C.writeCounter iactive 1
 
 -- | Setting the state to canceled.
 --   'Manager' eventually removes this without timeout action.
 cancel :: Handle -> IO ()
-cancel (Handle _ iactive) = I.writeIORef iactive Canceled
+cancel (Handle _ iactive) = C.writeCounter iactive 4
 
 -- | Setting the state to paused.
 --   'Manager' does not change the value.
 pause :: Handle -> IO ()
-pause (Handle _ iactive) = I.writeIORef iactive Paused
+pause (Handle _ iactive) = C.writeCounter iactive 3
 
 -- | Setting the paused state to active.
 --   This is an alias to 'tickle'.
diff --git a/warp.cabal b/warp.cabal
--- a/warp.cabal
+++ b/warp.cabal
@@ -1,5 +1,5 @@
 Name:                warp
-Version:             3.0.2
+Version:             3.0.2.1
 Synopsis:            A fast, light-weight web server for WAI applications.
 License:             MIT
 License-file:        LICENSE
@@ -52,6 +52,7 @@
                    , wai                       >= 3.0      && < 3.1
                    , text
                    , streaming-commons         >= 0.1.2
+                   , atomic-primops            >= 0.6
   if flag(network-bytestring)
       Build-Depends: network                   >= 2.2.1.5  && < 2.2.3
                    , network-bytestring        >= 0.1.3    && < 0.1.4
@@ -143,6 +144,7 @@
                    , text
                    , streaming-commons >= 0.1.1
                    , async
+                   , atomic-primops
 
   if (os(linux) || os(freebsd) || os(darwin)) && flag(allow-sendfilefd)
     Cpp-Options:   -DSENDFILEFD