diff --git a/test/Char8Spec.hs b/test/Char8Spec.hs
--- a/test/Char8Spec.hs
+++ b/test/Char8Spec.hs
@@ -2,107 +2,109 @@
 
 import qualified Data.Char as C
 import Data.Char8
+import Data.Word (Word8)
+import Word8Spec (word8ToChar)
 import Test.Hspec
 import Test.Hspec.QuickCheck
 
 spec :: Spec
 spec = do
     describe "isControl" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isControl c == C.isControl c
 
     describe "isSpace" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isSpace c == C.isSpace c
 
     describe "isLower" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isLower c == C.isLower c
 
     describe "isUpper" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isUpper c == C.isUpper c
 
     describe "isAlpha" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isAlpha c == C.isAlpha c
 
     describe "isAlphaNum" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isAlphaNum c == C.isAlphaNum c
 
     describe "isPrint" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isPrint c == C.isPrint c
 
     describe "isDigit" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isDigit c == C.isDigit c
 
     describe "isOctDigit" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isOctDigit c == C.isOctDigit c
 
     describe "isHexDigit" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isHexDigit c == C.isHexDigit c
 
     describe "isLetter" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isLetter c == C.isLetter c
 
     describe "isMark" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isMark c == C.isMark c
 
     describe "isNumber" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isNumber c == C.isNumber c
 
     describe "isPunctuation" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isPunctuation c == C.isPunctuation c
 
     describe "isSymbol" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isSymbol c == C.isSymbol c
 
     describe "isSeparator" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isSeparator c == C.isSeparator c
 
     describe "isAscii" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isAscii c == C.isAscii c
 
     describe "isLatin1" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isLatin1 c == C.isLatin1 c
 
     describe "isAsciiUpper" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isAsciiUpper c == C.isAsciiUpper c
 
     describe "isAsciiLower" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             isAsciiLower c == C.isAsciiLower c
 
     describe "toUpper" $ do
-        prop "behaves like model" $ prop_toUpper
+        prop "behaves like model" $ ensure $ prop_toUpper
 
     describe "toLower" $ do
-        prop "behaves like model" $ \c ->
+        prop "behaves like model" $ ensure $ \c ->
             toLower c == C.toLower c
 
     describe "toTitle" $ do
-        prop "behaves like model" $ prop_toTitle
+        prop "behaves like model" $ ensure $ prop_toTitle
 
 prop_toUpper :: Char -> Bool
 prop_toUpper c
   | c == _mu        = True
   | c == _ydieresis = True
   | otherwise       = toUpper c == C.toUpper c
-    
+
 prop_toTitle :: Char -> Bool
 prop_toTitle c
   | c == _mu  = True
@@ -114,3 +116,8 @@
 _mu, _ydieresis :: Char
 _mu        = '\xb5'
 _ydieresis = '\xff'
+
+----------------------------------------------------------------
+
+ensure :: (Char -> Bool) -> Word8 -> Bool
+ensure body w = body (word8ToChar w)
diff --git a/word8.cabal b/word8.cabal
--- a/word8.cabal
+++ b/word8.cabal
@@ -1,5 +1,5 @@
 Name:                   word8
-Version:                0.1.2
+Version:                0.1.3
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3