diff --git a/Network/HTTP/Conduit/Manager.hs b/Network/HTTP/Conduit/Manager.hs
--- a/Network/HTTP/Conduit/Manager.hs
+++ b/Network/HTTP/Conduit/Manager.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE BangPatterns #-}
 module Network.HTTP.Conduit.Manager
     ( Manager
     , ManagerSettings (..)
@@ -38,7 +39,8 @@
     , MonadThrow, MonadUnsafeIO
     )
 import Control.Concurrent (forkIO, threadDelay)
-import Data.Time (UTCTime, getCurrentTime, addUTCTime)
+import Data.Time (UTCTime (..), Day (..), DiffTime, getCurrentTime, addUTCTime)
+import Control.DeepSeq (deepseq)
 
 import Network (connectTo, PortID (PortNumber), HostName)
 import Network.Socket (socketToHandle)
@@ -161,8 +163,8 @@
             Nothing -> return () -- manager is closed
             Just toDestroy -> do
                 mapM_ safeConnClose toDestroy
+                !() <- I.atomicModifyIORef certCacheRef $ \x -> let y = flushStaleCerts now x in y `seq` (y, ())
                 loop
-        I.atomicModifyIORef certCacheRef $ \x -> (flushStaleCerts now x, ())
     findStaleWrap _ Nothing = (Nothing, Nothing)
     findStaleWrap isNotStale (Just m) =
         let (x, y) = findStale isNotStale m
@@ -189,10 +191,31 @@
         flushStaleCerts' (host', inner) =
             case mapMaybe flushStaleCerts'' $ Map.toList inner of
                 [] -> Nothing
-                pairs -> Just (host', Map.fromList $ take 10 pairs)
+                pairs ->
+                    let x = take 10 pairs
+                     in x `seqPairs` Just (host', Map.fromList x)
         flushStaleCerts'' (certs, expires)
             | expires > now = Just (certs, expires)
             | otherwise     = Nothing
+
+        seqPairs :: [(L.ByteString, UTCTime)] -> b -> b
+        seqPairs [] b = b
+        seqPairs (p:ps) b = p `seqPair` ps `seqPairs` b
+
+        seqPair :: (L.ByteString, UTCTime) -> b -> b
+        seqPair (lbs, utc) b = lbs `seqLBS` utc `seqUTC` b
+
+        seqLBS :: L.ByteString -> b -> b
+        seqLBS lbs b = L.length lbs `seq` b
+
+        seqUTC :: UTCTime -> b -> b
+        seqUTC (UTCTime day dt) b = day `seqDay` dt `seqDT` b
+
+        seqDay :: Day -> b -> b
+        seqDay (ModifiedJulianDay i) b = i `deepseq` b
+
+        seqDT :: DiffTime -> b -> b
+        seqDT = seq
 
 neToList :: NonEmptyList a -> [(UTCTime, a)]
 neToList (One a t) = [(t, a)]
diff --git a/http-conduit.cabal b/http-conduit.cabal
--- a/http-conduit.cabal
+++ b/http-conduit.cabal
@@ -1,5 +1,5 @@
 name:            http-conduit
-version:         1.4.1.3
+version:         1.4.1.4
 license:         BSD3
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -105,7 +105,7 @@
                  , time
                  , network
                  , wai
-                 , warp
+                 , warp >= 1.2.1
                  , socks
                  , http-types
                  , cookie
diff --git a/test/main.hs b/test/main.hs
--- a/test/main.hs
+++ b/test/main.hs
@@ -5,7 +5,8 @@
 import qualified Data.ByteString.Char8 as S8
 import Test.Hspec.HUnit ()
 import Test.HUnit
-import Network.Wai
+import Network.Wai hiding (requestBody)
+import qualified Network.Wai
 import Network.Wai.Handler.Warp (run)
 import Network.HTTP.Conduit
 import Control.Concurrent (forkIO, killThread, threadDelay)
@@ -24,6 +25,7 @@
 import qualified Data.Conduit.List as CL
 import qualified Data.Text.Encoding as TE
 import qualified Data.ByteString.Lazy as L
+import Blaze.ByteString.Builder (fromByteString)
 
 app :: Application
 app req =
@@ -114,6 +116,28 @@
                     , ("hello%20world%3f%23", "hello world?#")
                     ]
 
+    describe "chunked request body" $ do
+        it "works" $ do
+            tid <- forkIO echo
+            threadDelay 1000000
+            withManager $ \manager -> do
+                _ <- register $ killThread tid
+                let go bss = do
+                        let Just req1 = parseUrl "http://127.0.0.1:3007"
+                            src = sourceList $ map fromByteString bss
+                            lbs = L.fromChunks bss
+                        res <- httpLbs req1
+                            { method = "POST"
+                            , requestBody = RequestBodySourceChunked src
+                            } manager
+                        liftIO $ Network.HTTP.Conduit.responseStatus res @?= status200
+                        let ts = S.concat . L.toChunks
+                        liftIO $ ts (responseBody res) @?= ts lbs
+                mapM_ go
+                    [ ["hello", "world"]
+                    , replicate 500 "foo\003\n\r"
+                    ]
+
 overLongHeaders :: IO ()
 overLongHeaders = runTCPServer (ServerSettings 3004 HostAny) $ \_ sink ->
     src $$ sink
@@ -160,3 +184,8 @@
                 | x < 16 = toEnum $ x - 10 + (fromEnum 'A')
                 | otherwise = error $ "Invalid argument to showHex: " ++ show x
          in ['%', showHex' b, showHex' c]
+
+echo :: IO ()
+echo = run 3007 $ \req -> do
+    bss <- Network.Wai.requestBody req $$ CL.consume
+    return $ responseLBS status200 [] $ L.fromChunks bss