diff --git a/Codec/Archive/Zip.hs b/Codec/Archive/Zip.hs
--- a/Codec/Archive/Zip.hs
+++ b/Codec/Archive/Zip.hs
@@ -68,7 +68,8 @@
 import Control.Monad ( when, unless, zipWithM )
 import System.Directory ( getModificationTime )
 import System.IO ( stderr, hPutStrLn )
-import qualified Data.Hash.CRC32.GZip as CRC32
+import qualified Data.Digest.CRC32 as CRC32
+import qualified Data.Map as M
 
 #ifndef _WINDOWS
 import System.Posix.Files ( setFileTimes )
@@ -76,7 +77,6 @@
 
 -- from bytestring
 import qualified Data.ByteString.Lazy as B
-import Data.ByteString.Internal ( w2c )
 
 -- from utf8-string
 import Data.ByteString.Lazy.UTF8 ( toString, fromString )
@@ -160,7 +160,7 @@
 fromEntry :: Entry -> B.ByteString
 fromEntry entry =
   let uncompressedData = decompressData (eCompressionMethod entry) (eCompressedData entry)
-  in  if eCRC32 entry == computeCRC32 uncompressedData
+  in  if eCRC32 entry == CRC32.crc32 uncompressedData
          then uncompressedData
          else error "CRC32 mismatch"
 
@@ -178,7 +178,7 @@
         if uncompressedSize <= compressedSize
            then (NoCompression, contents, uncompressedSize)
            else (Deflate, compressedData, compressedSize)
-      crc32 = CRC32.calc_crc32 $ map w2c $ B.unpack contents
+      crc32 = CRC32.crc32 contents
   in  Entry { eRelativePath            = path
             , eCompressionMethod       = compressionMethod
             , eLastModified            = modtime
@@ -274,9 +274,6 @@
       dirParts = splitDirectories dir'
   in  drive ++ (concat (map (++ "/") dirParts)) ++ fn
 
-computeCRC32 :: B.ByteString -> Word32
-computeCRC32 = CRC32.calc_crc32 . map w2c . B.unpack
-
 -- | Uncompress a lazy bytestring.
 compressData :: CompressionMethod -> B.ByteString -> B.ByteString
 compressData Deflate       = Zlib.compress
@@ -406,7 +403,7 @@
 getArchive :: Get Archive
 getArchive = do
   locals <- many getLocalFile
-  files <- many (getFileHeader locals)
+  files <- many (getFileHeader (M.fromList locals))
   digSig <- lookAheadM getDigitalSignature
   endSig <- getWord32le
   unless (endSig == 0x06054b50) $ fail "Did not find end of central directory signature"
@@ -541,7 +538,7 @@
 -- >    extra field (variable size)
 -- >    file comment (variable size)
 
-getFileHeader :: [(Word32, B.ByteString)]  -- ^ list of (offset, content) pairs returned by getLocalFile
+getFileHeader :: M.Map Word32 B.ByteString -- ^ map of (offset, content) pairs returned by getLocalFile
               -> Get (Maybe Entry)
 getFileHeader locals = do
   sig <- lookAhead getWord32le
@@ -574,7 +571,7 @@
        fileName <- getLazyByteString (toEnum $ fromEnum fileNameLength)
        extraField <- getLazyByteString (toEnum $ fromEnum extraFieldLength)
        fileComment <- getLazyByteString (toEnum $ fromEnum fileCommentLength)
-       compressedData <- case lookup relativeOffset locals of
+       compressedData <- case (M.lookup relativeOffset locals) of
                          Just x  -> return x
                          Nothing -> fail $ "Unable to find data at offset " ++ show relativeOffset
        return $ Just $ Entry
diff --git a/Data/Hash/CRC32/GZip.hs b/Data/Hash/CRC32/GZip.hs
deleted file mode 100644
--- a/Data/Hash/CRC32/GZip.hs
+++ /dev/null
@@ -1,111 +0,0 @@
-{- arch-tag: GZIP CRC32 implementation in pure Haskell
-Copyright (C) 2004 John Goerzen <jgoerzen@complete.org>
-
-This program is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2 of the License, or
-(at your option) any later version.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program; if not, write to the Free Software
-Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
--}
-
-{- |
-   Module     : Data.Hash.CRC32.GZip
-   Copyright  : Copyright (C) 2004 John Goerzen
-   License    : GNU GPL, version 2 or later
-
-   Maintainer : John Goerzen <jgoerzen@complete.org> 
-   Stability  : provisional
-   Portability: portable
-
-CRC32 checksumming using the GZIP\/PKZIP algorithm as used in both
-ISO 3309 and section 8.1.1.6.2 of ITU-T V.42 and referenced in 
-RFC1952.
-
-Copyright (c) 2004 John Goerzen, jgoerzen\@complete.org
--}
-
-module Data.Hash.CRC32.GZip where
-
-import Data.Array
-import Data.Bits
-import Data.Word
-import Data.List
-import Data.Char
-
-update_crc :: Word32 -> Char -> Word32
-update_crc crc ch =
-    let c = crc `xor` 0xFFFFFFFF
-        newval = (gzipcrctab ! fromIntegral ((c `xor` fromIntegral (ord ch)) .&. 0xff))
-                 `xor` (c `shiftR` 8)
-        in
-        newval `xor` 0xFFFFFFFF
-
-update_crc_list :: Word32 -> [Char] -> Word32
-update_crc_list start list = foldl update_crc start list
-
-calc_crc32 :: [Char] -> Word32
-calc_crc32 s = update_crc_list 0 s
-        
-gzipcrctab :: Array Int Word32
-gzipcrctab = array (0,255) (zip [0..255]
-  [
-  0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
-  0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
-  0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
-  0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
-  0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
-  0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
-  0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
-  0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
-  0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
-  0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
-  0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
-  0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
-  0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
-  0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
-  0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
-  0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
-  0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
-  0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
-  0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
-  0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
-  0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
-  0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
-  0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
-  0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
-  0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
-  0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
-  0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
-  0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
-  0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
-  0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
-  0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
-  0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
-  0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
-  0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
-  0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
-  0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
-  0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
-  0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
-  0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
-  0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
-  0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
-  0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
-  0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
-  0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
-  0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
-  0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
-  0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
-  0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
-  0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
-  0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
-  0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
-  0x2d02ef8d ])
diff --git a/zip-archive.cabal b/zip-archive.cabal
--- a/zip-archive.cabal
+++ b/zip-archive.cabal
@@ -1,5 +1,5 @@
 Name:                zip-archive
-Version:             0.1.1.1
+Version:             0.1.1.2
 Cabal-version:       >= 1.2
 Build-type:          Simple
 Synopsis:            Library for creating and modifying zip archives.
@@ -25,11 +25,10 @@
     Build-depends:   base >= 3, pretty, containers
   else
     Build-depends:   base < 3
-  Build-depends:     binary, zlib, filepath, directory, bytestring >= 0.9.0, array, mtl, utf8-string >= 0.3.1, old-time
+  Build-depends:     binary, zlib, filepath, directory, bytestring >= 0.9.0, array, mtl, utf8-string >= 0.3.1, old-time, digest >= 0.0.0.1
   Exposed-modules:   Codec.Archive.Zip
-  Other-modules:     Data.Hash.CRC32.GZip
   Hs-Source-Dirs:    .
-  Ghc-Options:       -Wall
+  Ghc-Options:       -Wall -O2
   Extensions:        CPP
   if os(windows)
     cpp-options:     -D_WINDOWS
@@ -42,4 +41,4 @@
   else
     Buildable:       False
   Main-is:           Zip.hs
-  Ghc-Options:       -Wall
+  Ghc-Options:       -Wall -O2
