diff --git a/Network/Wai/Application/Classic.hs b/Network/Wai/Application/Classic.hs
--- a/Network/Wai/Application/Classic.hs
+++ b/Network/Wai/Application/Classic.hs
@@ -5,20 +5,13 @@
 module Network.Wai.Application.Classic (
   -- * Types
     AppSpec(..)
-  , Logger
   , FileInfo(..)
   -- * Files
   , FileRoute(..), fileApp
   -- * CGI
   , CgiRoute(..), cgiApp
-  -- * Utilities for logging
-  , NumericAddress, showSockAddr
-  , FieldKey
-  , lookupRequestField, lookupRequestField'
   ) where
 
 import Network.Wai.Application.Classic.CGI
 import Network.Wai.Application.Classic.File
 import Network.Wai.Application.Classic.Types
-import Network.Wai.Application.Classic.Utils
-import Network.Wai.Application.Classic.Header
diff --git a/Network/Wai/Application/Classic/CGI.hs b/Network/Wai/Application/Classic/CGI.hs
--- a/Network/Wai/Application/Classic/CGI.hs
+++ b/Network/Wai/Application/Classic/CGI.hs
@@ -22,6 +22,7 @@
 import Network.Wai.Application.Classic.Header
 import Network.Wai.Application.Classic.Types
 import Network.Wai.Application.Classic.Utils
+import Network.Wai.Logger.Utils
 import System.IO
 import System.Process
 
@@ -85,7 +86,7 @@
     toBuilder = EL.map fromByteString
     emptyBody = EB.isolate 0
     response build status hs = toBuilder =$ build status hs
-    check hs = lookupField fkContentType hs >> case lookupField "status" hs of
+    check hs = lookup fkContentType hs >> case lookup "status" hs of
         Nothing -> Just (status200, hs)
         Just l  -> toStatus l >>= \s -> Just (s,hs')
       where
@@ -111,9 +112,9 @@
       , ("QUERY_STRING",      query req)
       ]
     headers = requestHeaders req
-    addLength = addEnv "CONTENT_LENGTH" $ lookupField fkContentLength headers
-    addType   = addEnv "CONTENT_TYPE" $ lookupField fkContentType headers
-    addCookie = addEnv "HTTP_COOKIE" $ lookupField fkCookie headers
+    addLength = addEnv "CONTENT_LENGTH" $ lookup fkContentLength headers
+    addType   = addEnv "CONTENT_TYPE" $ lookup fkContentType headers
+    addCookie = addEnv "HTTP_COOKIE" $ lookup fkCookie headers
     query = BS.unpack . safeTail . rawQueryString
       where
         safeTail "" = ""
diff --git a/Network/Wai/Application/Classic/Field.hs b/Network/Wai/Application/Classic/Field.hs
--- a/Network/Wai/Application/Classic/Field.hs
+++ b/Network/Wai/Application/Classic/Field.hs
@@ -20,7 +20,7 @@
 
 ----------------------------------------------------------------
 
-languages :: Request -> [ByteString]
+languages :: Request -> [Ascii]
 languages req = maybe [] parseLang $ lookupRequestField fkAcceptLanguage req
 
 ifModifiedSince :: Request -> Maybe HTTPDate
@@ -32,7 +32,7 @@
 ifRange :: Request -> Maybe HTTPDate
 ifRange = lookupAndParseDate fkIfRange
 
-lookupAndParseDate :: ByteString -> Request -> Maybe HTTPDate
+lookupAndParseDate :: FieldKey -> Request -> Maybe HTTPDate
 lookupAndParseDate key req = lookupRequestField key req >>= parseHTTPDate
 
 ----------------------------------------------------------------
diff --git a/Network/Wai/Application/Classic/Header.hs b/Network/Wai/Application/Classic/Header.hs
--- a/Network/Wai/Application/Classic/Header.hs
+++ b/Network/Wai/Application/Classic/Header.hs
@@ -2,8 +2,6 @@
 
 module Network.Wai.Application.Classic.Header where
 
-import Data.ByteString (ByteString)
-import Data.ByteString.Char8 ()
 import Data.CaseInsensitive
 import Data.Maybe
 import Network.HTTP.Types
@@ -12,10 +10,10 @@
 ----------------------------------------------------------------
 
 -- | Header field key. This must be lower case.
-type FieldKey = ByteString
+type FieldKey = CI Ascii
 
 -- | A type for look-up key.
-fkAcceptLanguage :: ByteString
+fkAcceptLanguage :: FieldKey
 fkAcceptLanguage = "accept-language"
 
 -- | Look-up key for Range:.
@@ -63,25 +61,16 @@
 {-|
   Looking up a header in 'Request'.
 -}
-lookupRequestField :: FieldKey -> Request -> Maybe ByteString
-lookupRequestField x req = lookupField x hdrs
+lookupRequestField :: FieldKey -> Request -> Maybe Ascii
+lookupRequestField x req = lookup x hdrs
   where
     hdrs = requestHeaders req
 
 {-|
   Looking up a header in 'Request'. If the header does not exist,
-  empty 'ByteString' is returned.
+  empty 'Ascii' is returned.
 -}
-lookupRequestField' :: FieldKey -> Request -> ByteString
-lookupRequestField' x req = fromMaybe "" $ lookupField x hdrs
+lookupRequestField' :: FieldKey -> Request -> Ascii
+lookupRequestField' x req = fromMaybe "" $ lookup x hdrs
   where
     hdrs = requestHeaders req
-
-{-|
-  Looking up a header in 'RequestHeaders'.
--}
-lookupField :: FieldKey -> RequestHeaders -> Maybe ByteString
-lookupField x ((key, val):kvs)
-  | x == foldedCase key = Just val
-  | otherwise           = lookupField x kvs
-lookupField _ []        = Nothing
diff --git a/Network/Wai/Application/Classic/MaybeIter.hs b/Network/Wai/Application/Classic/MaybeIter.hs
--- a/Network/Wai/Application/Classic/MaybeIter.hs
+++ b/Network/Wai/Application/Classic/MaybeIter.hs
@@ -39,7 +39,7 @@
     case v of
       Nothing -> nothing
       Just x  -> act x
-      
+
 (|>|) :: MaybeIter a -> (a -> MaybeIter b) -> MaybeIter b
 a |>| act = do
     v <- a
diff --git a/Network/Wai/Application/Classic/Types.hs b/Network/Wai/Application/Classic/Types.hs
--- a/Network/Wai/Application/Classic/Types.hs
+++ b/Network/Wai/Application/Classic/Types.hs
@@ -4,7 +4,7 @@
 import qualified Data.ByteString.Lazy as BL (ByteString)
 import Network.HTTP.Date
 import Network.HTTP.Types
-import Network.Wai
+import Network.Wai.Logger.Prefork
 
 data AppSpec = AppSpec {
     -- | Name specified to Server: in HTTP response.
@@ -14,12 +14,10 @@
     -- | Whether this is an HTML or not.
   , isHTML :: ByteString -> Bool
     -- | A function for logging. The third argument is a body size.
-  , logger :: Logger
+  , logger :: ApacheLogger
     -- | A function to obtain information about a file.
   , getFileInfo :: ByteString -> IO (Maybe FileInfo)
   }
-
-type Logger = Request -> Status -> Maybe Integer -> IO ()
 
 data FileInfo = FileInfo {
     fileInfoName :: FilePath
diff --git a/Network/Wai/Application/Classic/Utils.hs b/Network/Wai/Application/Classic/Utils.hs
--- a/Network/Wai/Application/Classic/Utils.hs
+++ b/Network/Wai/Application/Classic/Utils.hs
@@ -1,63 +1,14 @@
 {-# LANGUAGE OverloadedStrings #-}
 
 module Network.Wai.Application.Classic.Utils (
-    NumericAddress, showSockAddr
-  , hasTrailingPathSeparator, pathSep
+    hasTrailingPathSeparator, pathSep
   , (+++), (</>)
   ) where
 
-import Data.Bits
 import Data.ByteString (ByteString)
 import qualified Data.ByteString as BS
 import Data.ByteString.Char8 ()
 import Data.Word
-import Network.Socket (SockAddr(..))
-import System.ByteOrder
-import Text.Printf
-
-{-|
-  A type for IP address in numeric string representation.
--}
-type NumericAddress = String
-
-showIPv4 :: Word32 -> Bool -> NumericAddress
-showIPv4 w32 little
-    | little    = show b1 ++ "." ++ show b2 ++ "." ++ show b3 ++ "." ++ show b4
-    | otherwise = show b4 ++ "." ++ show b3 ++ "." ++ show b2 ++ "." ++ show b1
-  where
-    t1 = w32
-    t2 = shift t1 (-8)
-    t3 = shift t2 (-8)
-    t4 = shift t3 (-8)
-    b1 = t1 .&. 0x000000ff
-    b2 = t2 .&. 0x000000ff
-    b3 = t3 .&. 0x000000ff
-    b4 = t4 .&. 0x000000ff
-
-showIPv6 :: (Word32,Word32,Word32,Word32) -> String
-showIPv6 (w1,w2,w3,w4) =
-    printf "%x:%x:%x:%x:%x:%x:%x:%x" s1 s2 s3 s4 s5 s6 s7 s8
-  where
-    (s1,s2) = foo w1
-    (s3,s4) = foo w2
-    (s5,s6) = foo w3
-    (s7,s8) = foo w4
-    foo w = (h1,h2)
-      where
-        h1 = w .&. 0x0000ffff
-        h2 = shift w (-16) .&. 0x0000ffff
-{-|
-  Convert 'SockAddr' to 'NumericAddress'. If the address is
-  an IPv4-embedded IPv6 address, the IPv4 is extracted.
--}
--- HostAddr is network byte order.
--- HostAddr6 is host byte order.
-showSockAddr :: SockAddr -> NumericAddress
-showSockAddr (SockAddrInet _ addr4)                       = showIPv4 addr4 (byteOrder == LittleEndian)
-showSockAddr (SockAddrInet6 _ _ (0,0,0x0000ffff,addr4) _) = showIPv4 addr4 False
-showSockAddr (SockAddrInet6 _ _ (0,0,0,1) _)              = "::1"
-showSockAddr (SockAddrInet6 _ _ addr6 _)                  = showIPv6 addr6
-showSockAddr _                                            = "unknownSocket"
 
 pathSep :: Word8
 pathSep = 47
diff --git a/wai-app-file-cgi.cabal b/wai-app-file-cgi.cabal
--- a/wai-app-file-cgi.cabal
+++ b/wai-app-file-cgi.cabal
@@ -1,5 +1,5 @@
 Name:                   wai-app-file-cgi
-Version:                0.3.1
+Version:                0.3.2
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -34,8 +34,8 @@
                         containers, attoparsec,
                         wai, enumerator >= 0.4.9,
                         bytestring, blaze-builder,
-                        wai-app-static, http-types, http-date,
-                        case-insensitive, static-hash, byteorder
+                        wai-app-static >= 0.3, http-types, http-date,
+                        case-insensitive, static-hash, wai-logger
 Source-Repository head
   Type:                 git
   Location:             git://github.com/kazu-yamamoto/wai-app-file-cgi.git