diff --git a/Data/UnixTime.hs b/Data/UnixTime.hs
--- a/Data/UnixTime.hs
+++ b/Data/UnixTime.hs
@@ -8,7 +8,7 @@
   , parseUnixTimeGMT
   , formatUnixTime
   , formatUnixTimeGMT
-  -- * Fromat
+  -- * Format
   , Format
   , webDateFormat
   , mailDateFormat
diff --git a/test/UnixTimeSpec.hs b/test/UnixTimeSpec.hs
--- a/test/UnixTimeSpec.hs
+++ b/test/UnixTimeSpec.hs
@@ -1,19 +1,21 @@
 {-# LANGUAGE OverloadedStrings, FlexibleInstances #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 
-module UnixTimeSpec where
+module UnixTimeSpec (main, spec) where
 
 import Data.ByteString (ByteString)
 import qualified Data.ByteString.Char8 as BS
 import Data.Time
 import Data.Time.Clock.POSIX (posixSecondsToUTCTime)
 import Data.UnixTime
-import System.IO.Unsafe (unsafePerformIO)
 import System.Locale (defaultTimeLocale)
 import Test.Hspec
 import Test.Hspec.QuickCheck (prop)
 import Test.QuickCheck
 
+main :: IO ()
+main = hspec spec
+
 instance Arbitrary UnixTime where
     arbitrary = do
         a <- choose (0,4294967295) :: Gen Int
@@ -24,16 +26,15 @@
               }
         return ut
 
-currentTimeZone :: TimeZone
-currentTimeZone = unsafePerformIO getCurrentTimeZone
-
 spec :: Spec
 spec = do
     describe "formatUnixTime" $
-        prop "behaves like the model" $ \ut ->
+        prop "behaves like the model" $ \ut -> do
             let ours = formatUnixTime mailDateFormat ut
-                model = formatMailModel (toUTCTime ut) currentTimeZone
-            in ours == model
+                utcTime = toUTCTime ut
+            timeZone <- getTimeZone utcTime
+            let model = formatMailModel utcTime timeZone
+            ours `shouldBe` model
 
     describe "parseUnixTimeGMT & formatUnixTimeGMT" $
         prop "inverses the result" $ \ut@(UnixTime sec _) ->
diff --git a/unix-time.cabal b/unix-time.cabal
--- a/unix-time.cabal
+++ b/unix-time.cabal
@@ -1,5 +1,5 @@
 Name:                   unix-time
-Version:                0.1.5
+Version:                0.1.6
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -43,7 +43,7 @@
   Other-Modules:        UnixTimeSpec
   Build-Depends:        base
                       , bytestring
-                      , hspec
+                      , hspec >= 1.5
                       , old-locale
                       , old-time
                       , QuickCheck