diff --git a/src/Network/Minio/PutObject.hs b/src/Network/Minio/PutObject.hs
index 845ab45..33132b2 100644
--- a/src/Network/Minio/PutObject.hs
+++ b/src/Network/Minio/PutObject.hs
@@ -7,11 +7,11 @@ module Network.Minio.PutObject
 
 
 import qualified Data.ByteString as B
-import qualified Data.ByteString.Lazy as LB
 import qualified Data.Conduit as C
 import           Data.Conduit.Binary (sourceHandleRange)
 import qualified Data.Conduit.Binary as CB
 import qualified Data.Conduit.Combinators as CC
+import qualified Data.Conduit.List as CL
 import qualified Data.List as List
 import qualified Data.Map.Strict as Map
 
@@ -144,40 +144,29 @@ sequentialMultipartUpload b o sizeMay src = do
   uploadId <- maybe (newMultipartUpload b o []) return uidMay
 
   -- upload parts in loop
-  uploadedParts <- uploadPartsSequentially b o uploadId pmap sizeMay src
+  let partSizes = selectPartSizes $ maybe maxObjectSize identity sizeMay
+      (pnums, _, sizes) = List.unzip3 partSizes
+  uploadedParts <- src
+              C..| chunkBSConduit sizes
+              C..| CL.map PayloadBS
+              C..| checkAndUpload uploadId pmap pnums
+              C.$$ CC.sinkList
 
   -- complete multipart upload
   completeMultipartUpload b o uploadId uploadedParts
 
-uploadPartsSequentially :: Bucket -> Object -> UploadId
-                        -> Map PartNumber ListPartInfo -> Maybe Int64
-                        -> C.Source Minio ByteString -> Minio [PartInfo]
-uploadPartsSequentially b o uid pmap sizeMay src' = do
-  let
-    rSrc = C.newResumableSource src'
-    partSizes = selectPartSizes $ maybe maxObjectSize identity sizeMay
-
-  loopIt rSrc partSizes []
-
   where
-    -- make a sink that consumes only `s` bytes
-    limitedSink s = CB.isolate (fromIntegral s) C.=$= CB.sinkLbs
-
-    loopIt _ [] uparts = return $ reverse uparts
-    loopIt src ((n, _, size):ps) uparts = do
-      (newSrc, buf) <- src C.$$++ (limitedSink size)
-
-      let buflen = LB.length buf
-          payload = PayloadBS $ LB.toStrict buf
-
-      partMay <- checkUploadNeeded payload n pmap
-
-      if buflen == 0
-        then return $ reverse uparts
-        else do pInfo <- maybe (putObjectPart b o uid n [] payload)
-                         return partMay
-                loopIt newSrc ps (pInfo:uparts)
-
+    checkAndUpload _ _ [] = return ()
+    checkAndUpload uid pmap (pn:pns) = do
+      payloadMay <- C.await
+      case payloadMay of
+        Nothing -> return ()
+        Just payload -> do partMay <- lift $ checkUploadNeeded payload pn pmap
+                           pinfo <- maybe
+                                    (lift $ putObjectPart b o uid pn [] payload)
+                                    return partMay
+                           C.yield pinfo
+                           checkAndUpload uid pmap pns
 
 -- | Looks for incomplete uploads for an object. Returns the first one
 -- if there are many.
diff --git a/src/Network/Minio/Utils.hs b/src/Network/Minio/Utils.hs
index 0f91eff..31bc0e1 100644
--- a/src/Network/Minio/Utils.hs
+++ b/src/Network/Minio/Utils.hs
@@ -3,9 +3,11 @@ module Network.Minio.Utils where
 import qualified Control.Concurrent.Async.Lifted as A
 import qualified Control.Concurrent.QSem as Q
 import qualified Control.Exception.Lifted as ExL
+import qualified Control.Monad.Catch as MC
 import           Control.Monad.Trans.Control (liftBaseOp_, StM)
 import qualified Control.Monad.Trans.Resource as R
-import qualified Control.Monad.Catch as MC
+
+import qualified Data.ByteString as B
 import qualified Data.Conduit as C
 import           Data.Text.Encoding.Error (lenientDecode)
 import qualified Network.HTTP.Client as NClient
@@ -136,3 +138,22 @@ mkQuery k mv = (k,) <$> mv
 -- don't use it with mandatory query params with empty value.
 mkOptionalParams :: [(Text, Maybe Text)] -> HT.Query
 mkOptionalParams params = HT.toQuery $ (uncurry  mkQuery) <$> params
+
+chunkBSConduit :: (Monad m, Integral a)
+               => [a] -> C.Conduit ByteString m ByteString
+chunkBSConduit s = loop 0 [] s
+  where
+    loop _ _ [] = return ()
+    loop n readChunks (size:sizes) = do
+      bsMay <- C.await
+      case bsMay of
+        Nothing -> if n > 0
+                   then C.yield $ B.concat readChunks
+                   else return ()
+        Just bs -> if n + fromIntegral (B.length bs) >= size
+                   then do let (a, b) = B.splitAt (fromIntegral $ size - n) bs
+                               chunkBS = B.concat $ readChunks ++ [a]
+                           C.yield chunkBS
+                           loop (fromIntegral $ B.length b) [b] sizes
+                   else loop (n + fromIntegral (B.length bs))
+                        (readChunks ++ [bs]) (size:sizes)
diff --git a/test/Spec.hs b/test/Spec.hs
index 06b569f..db77959 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -7,7 +7,6 @@ import           Lib.Prelude
 
 import           System.Directory (getTemporaryDirectory)
 import qualified System.IO as SIO
-import           System.IO.Temp (openBinaryTempFile, withSystemTempDirectory)
 
 import qualified Control.Monad.Trans.Resource as R
 import qualified Data.ByteString as BS
@@ -225,10 +224,7 @@ liveServerUnitTests = testGroup "Unit tests against a live server"
   , funTestWithBucket "multipart" $ \step bucket -> do
 
       step "upload large object"
-      -- fPutObject bucket "big" "/tmp/large"
-      -- putObject bucket "big" ("/dev/zero")
-      etag <- putObject bucket "big" (ODFile "/dev/zero" $ Just $ 1024*1024*100)
-      traceShowM etag
+      void $ putObject bucket "big" (ODFile "/dev/zero" $ Just $ 1024*1024*100)
 
       step "cleanup"
       deleteObject bucket "big"
@@ -245,7 +241,7 @@ liveServerUnitTests = testGroup "Unit tests against a live server"
       step "put object parts 1..10"
       inputFile <- mkRandFile mb15
       h <- liftIO $ SIO.openBinaryFile inputFile SIO.ReadMode
-      forM [1..10] $ \pnum ->
+      forM_ [1..10] $ \pnum ->
         putObjectPart bucket object uid pnum [] $ PayloadH h 0 mb15
 
       step "fetch list parts"
@@ -296,7 +292,7 @@ liveServerUnitTests = testGroup "Unit tests against a live server"
       step "put object parts 1..10"
       inputFile <- mkRandFile mb15
       h <- liftIO $ SIO.openBinaryFile inputFile SIO.ReadMode
-      forM [1..10] $ \pnum ->
+      forM_ [1..10] $ \pnum ->
         putObjectPart bucket object uid pnum [] $ PayloadH h 0 mb15
 
       step "fetch list parts"