diff --git a/ascii-progress.cabal b/ascii-progress.cabal
--- a/ascii-progress.cabal
+++ b/ascii-progress.cabal
@@ -1,5 +1,5 @@
 name:                ascii-progress
-version:             0.3.2.0
+version:             0.3.3.0
 synopsis:            A simple progress bar for the console.
 description:
     A simple Haskell progress bar for the console. Heavily borrows from TJ
@@ -17,6 +17,7 @@
 category:            System
 build-type:          Simple
 cabal-version:       >=1.10
+
 source-repository head
   type:     git
   location: git://github.com/yamadapc/haskell-ascii-progress
@@ -51,6 +52,23 @@
                      , time >= 1.4.0.1
     hs-source-dirs:    lib
                      , bin
+
+executable npm-example
+  main-is:             NpmExample.hs
+  default-language:    Haskell2010
+
+  if !flag(examples)
+    buildable: False
+  else
+    buildable: True
+    build-depends:     concurrent-output >= 1.7
+                     , async >= 2.0.1.5
+                     , base >=4 && <5
+                     , data-default >= 0.5.3
+                     , time >= 1.4.0.1
+    hs-source-dirs:    lib
+                     , bin
+
 
 executable download-example
   main-is:             DownloadExample.hs
diff --git a/bin/NpmExample.hs b/bin/NpmExample.hs
new file mode 100644
--- /dev/null
+++ b/bin/NpmExample.hs
@@ -0,0 +1,19 @@
+import           Control.Concurrent           (threadDelay)
+import           Control.Monad                (unless)
+import           System.Console.AsciiProgress
+
+main :: IO ()
+main = displayConsoleRegions $ do
+    pg <- newProgressBar def { pgWidth = 100
+                             , pgPendingChar = '░'
+                             , pgCompletedChar = '█'
+                             , pgFormat = "Working ╢:bar╟"
+                             }
+    loop pg
+  where
+    loop pg = do
+        b <- isComplete pg
+        unless b $ do
+            threadDelay $ 200 * 1000
+            tick pg
+            loop pg
diff --git a/lib/System/Console/AsciiProgress/Internal.hs b/lib/System/Console/AsciiProgress/Internal.hs
--- a/lib/System/Console/AsciiProgress/Internal.hs
+++ b/lib/System/Console/AsciiProgress/Internal.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE MagicHash       #-}
 {-# LANGUAGE RecordWildCards #-}
-{-# LANGUAGE UnboxedTuples   #-}
 module System.Console.AsciiProgress.Internal
   where
 
@@ -187,5 +186,7 @@
         if success
            then return v
            else readMVar mv
-    Just o -> return o
+    Just o -> do
+        _ <- tryPutMVar mv o
+        return o