diff --git a/src/Control/Concurrent/Thread/Storage.hs b/src/Control/Concurrent/Thread/Storage.hs
--- a/src/Control/Concurrent/Thread/Storage.hs
+++ b/src/Control/Concurrent/Thread/Storage.hs
@@ -2,7 +2,7 @@
 {-# LANGUAGE UnliftedFFITypes #-}
 {-# LANGUAGE UnboxedTuples #-}
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE Strict #-}
+{-# LANGUAGE BangPatterns #-}
 -- | A perilous implementation of thread-local storage for Haskell.
 -- This module uses a fair amount of GHC internals to enable performing
 -- lookups of context for any threads that are alive. Caution should be
@@ -158,13 +158,13 @@
 -- | The most general function in this library. Update a 'ThreadStorageMap' on a given thread,
 -- with the ability to add or remove values and return some sort of result.
 updateOnThread :: MonadIO m => ThreadStorageMap a -> ThreadId -> (Maybe a -> (Maybe a, b)) -> m b
-updateOnThread tsm tid f = liftIO $ do
+updateOnThread tsm tid f = liftIO $ mask_ $ do
   -- ^ We mask here in order to ensure that the finalizer will always be created
   (isNewThreadEntry, result) <- atomicModifyStripe tsm threadAsInt $ \m -> 
     let (resultWithNewThreadDetection, m') = 
           I.alterF 
             (\x -> case f x of
-              (x', y) -> ((isNothing x && isJust x', y), x')
+              (!x', !y) -> ((isNothing x && isJust x', y), x')
             ) 
             threadAsInt
             m
diff --git a/thread-utils-context.cabal b/thread-utils-context.cabal
--- a/thread-utils-context.cabal
+++ b/thread-utils-context.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           thread-utils-context
-version:        0.3.0.0
+version:        0.3.0.1
 synopsis:       Garbage-collected thread local storage
 description:    Please see the README on GitHub at <https://github.com/iand675/thread-utils-context#readme>
 category:       Concurrency