diff --git a/Database/MongoDB/GridFS.hs b/Database/MongoDB/GridFS.hs
index c1d03d0..02953b4 100644
--- a/Database/MongoDB/GridFS.hs
+++ b/Database/MongoDB/GridFS.hs
@@ -3,7 +3,7 @@
 -- | MongoDB GridFS implementation
 {-# LANGUAGE OverloadedStrings, RecordWildCards, NamedFieldPuns, TupleSections, FlexibleContexts, FlexibleInstances, UndecidableInstances, MultiParamTypeClasses, GeneralizedNewtypeDeriving, StandaloneDeriving, TypeSynonymInstances, TypeFamilies, CPP, RankNTypes #-}
 
-module Database.MongoDB.GridFS 
+module Database.MongoDB.GridFS
   ( Bucket
   , files, chunks
   , File
@@ -24,11 +24,11 @@ module Database.MongoDB.GridFS
   where
 
 import Control.Applicative((<$>))
-import Control.Concurrent(forkIO)
+
 import Control.Monad(when)
 import Control.Monad.IO.Class
 import Control.Monad.Trans(MonadTrans, lift)
-import Control.Monad.Trans.Resource(MonadResource(..))
+
 import Data.Conduit
 import Data.Digest.Pure.MD5
 import Data.Int
@@ -40,13 +40,17 @@ import Prelude
 import qualified Data.Bson as B
 import qualified Data.ByteString as S
 import qualified Data.ByteString.Lazy as L
-import qualified Data.Conduit.Binary as BI
-import qualified Data.Conduit.List as CL
+
 
 defaultChunkSize :: Int64
 -- ^ The default chunk size is 256 kB
 defaultChunkSize = 256 * 1024
 
+-- magic constant for the
+md5BlockSizeInBytes :: Int
+md5BlockSizeInBytes = 64
+
+
 data Bucket = Bucket {files :: Text, chunks :: Text}
 -- ^ Files are stored in "buckets". You open a bucket with openDefaultBucket or openBucket
 
@@ -125,12 +129,12 @@ data FileWriter = FileWriter
   , fwAcc :: L.ByteString
   , fwMd5Context :: MD5Context
   , fwMd5acc :: L.ByteString
-  } 
+  }
 
 -- Finalize file, calculating md5 digest, saving the last chunk, and creating the file in the bucket
 finalizeFile :: (Monad m, MonadIO m) => Text -> FileWriter -> Action m File
 finalizeFile filename (FileWriter chunkSize bucket files_id i size acc md5context md5acc) = do
-  let md5digest = md5Finalize md5context (L.toStrict md5acc)
+  let md5digest = finalizeMD5 md5context (L.toStrict md5acc)
   when (L.length acc > 0) $ putChunk bucket files_id i acc
   timestamp <- liftIO $ getCurrentTime
   let doc = [ "_id" =: files_id
@@ -140,30 +144,42 @@ finalizeFile filename (FileWriter chunkSize bucket files_id i size acc md5contex
             , "chunkSize" =: chunkSize
             , "filename" =: filename
             ]
+  _ <- liftIO $ putStrLn $ "md5 : " ++ (show md5digest)
   insert_ (files bucket) doc
   return $ File bucket doc
 
+-- finalize the remainder and return the MD5Digest.
+finalizeMD5 :: MD5Context -> S.ByteString -> MD5Digest
+finalizeMD5 ctx rest =
+  md5Finalize ctx2 (S.drop lu rest) -- can only handle max md5BlockSizeInBytes length
+  where
+    l = S.length rest
+    r = l `mod` md5BlockSizeInBytes
+    lu = l - r
+    ctx2 = md5Update ctx (S.take lu rest)
+
 -- Write as many chunks as can be written from the file writer
 writeChunks :: (Monad m, MonadIO m) => FileWriter -> L.ByteString -> Action m FileWriter
-writeChunks (FileWriter chunkSize bucket files_id i size acc md5context md5acc) chunk = do
-  -- Update md5 context
-  let md5BlockLength = fromIntegral $ untag (blockLength :: Tagged MD5Digest Int)
-  let md5acc_temp = (md5acc `L.append` chunk)
-  let (md5context', md5acc') = 
-        if (L.length md5acc_temp < md5BlockLength)
-        then (md5context, md5acc_temp)
-        else let numBlocks = L.length md5acc_temp `div` md5BlockLength
-                 (current, rest) = L.splitAt (md5BlockLength * numBlocks) md5acc_temp
-             in (md5Update md5context (L.toStrict current), rest)
-  -- Update chunks
-  let size' = (size + L.length chunk)
-  let acc_temp = (acc `L.append` chunk)
-  if (L.length acc_temp < chunkSize)
-    then return (FileWriter chunkSize bucket files_id i size' acc_temp md5context' md5acc')
-    else do
-      let (chunk, acc') = L.splitAt chunkSize acc_temp
-      putChunk bucket files_id i chunk
-      writeChunks (FileWriter chunkSize bucket files_id (i+1) size' acc' md5context' md5acc') L.empty
+writeChunks (FileWriter chunkSize bucket files_id i size acc md5context md5acc) chunk =
+  do
+    -- Update md5 context
+    let md5BlockLength = fromIntegral $ untag (blockLength :: Tagged MD5Digest Int)
+    let md5acc_temp = (md5acc `L.append` chunk)
+    let (md5context', md5acc') =
+          if (L.length md5acc_temp < md5BlockLength)
+          then (md5context, md5acc_temp)
+          else let numBlocks = L.length md5acc_temp `div` md5BlockLength
+                   (current, rest) = L.splitAt (md5BlockLength * numBlocks) md5acc_temp
+               in (md5Update md5context (L.toStrict current), rest)
+    -- Update chunks
+    let size' = (size + L.length chunk)
+    let acc_temp = (acc `L.append` chunk)
+    if (L.length acc_temp < chunkSize)
+      then return (FileWriter chunkSize bucket files_id i size' acc_temp md5context' md5acc')
+      else do
+            let (chunk, acc') = L.splitAt chunkSize acc_temp
+            putChunk bucket files_id i chunk
+            writeChunks (FileWriter chunkSize bucket files_id (i+1) size' acc' md5context' md5acc') L.empty
 
 sinkFile :: (Monad m, MonadIO m) => Bucket -> Text -> Consumer S.ByteString (Action m) File
 -- ^ A consumer that creates a file in the bucket and puts all consumed data in it