diff --git a/Database/MongoDB/Internal/Util.hs b/Database/MongoDB/Internal/Util.hs
--- a/Database/MongoDB/Internal/Util.hs
+++ b/Database/MongoDB/Internal/Util.hs
@@ -97,7 +97,7 @@
 updateAssocs key valu assocs = case back of [] -> (key, valu) : front; _ : back' -> front ++ (key, valu) : back'
 	where (front, back) = break ((key ==) . fst) assocs
 
-bitOr :: (Bits a) => [a] -> a
+bitOr :: (Num a, Bits a) => [a] -> a
 -- ^ bit-or all numbers together
 bitOr = foldl (.|.) 0
 
diff --git a/Database/MongoDB/Query.hs b/Database/MongoDB/Query.hs
--- a/Database/MongoDB/Query.hs
+++ b/Database/MongoDB/Query.hs
@@ -1,6 +1,6 @@
 -- | Query and update documents
 
-{-# LANGUAGE OverloadedStrings, RecordWildCards, NamedFieldPuns, TupleSections, FlexibleContexts, FlexibleInstances, UndecidableInstances, MultiParamTypeClasses, GeneralizedNewtypeDeriving, StandaloneDeriving, TypeSynonymInstances, TypeFamilies #-}
+{-# LANGUAGE OverloadedStrings, RecordWildCards, NamedFieldPuns, TupleSections, FlexibleContexts, FlexibleInstances, UndecidableInstances, MultiParamTypeClasses, GeneralizedNewtypeDeriving, StandaloneDeriving, TypeSynonymInstances, TypeFamilies, CPP #-}
 
 module Database.MongoDB.Query (
 	-- * Monad
@@ -47,8 +47,13 @@
 import Data.Maybe (listToMaybe, catMaybes)
 import Data.Word (Word32)
 
-import Control.Concurrent.MVar.Lifted (MVar, newMVar, addMVarFinalizer,
+#if MIN_VERSION_base(4,6,0)
+import Control.Concurrent.MVar.Lifted (MVar, newMVar, mkWeakMVar,
                                        readMVar, modifyMVar)
+#else
+import Control.Concurrent.MVar.Lifted (MVar, newMVar, addMVarFinalizer,
+                                         readMVar, modifyMVar)
+#endif
 import Control.Monad.Base (MonadBase(liftBase))
 import Control.Monad.Error (ErrorT, Error(..), MonadError, runErrorT,
                             throwError)
@@ -60,8 +65,9 @@
                                     MonadTransControl(..), StM, StT,
                                     defaultLiftBaseWith, defaultRestoreM)
 import Control.Monad.Writer (WriterT, Monoid)
-import Data.Bson (Document, Field(..), Label, Value(String,Doc), Javascript,
-                  at, valueAt, lookup, look, genObjectId, (=:), (=?))
+import Data.Bson (Document, Field(..), Label, Val, Value(String,Doc),
+                  Javascript, at, valueAt, lookup, look, genObjectId, (=:),
+                  (=?))
 import Data.Text (Text)
 import qualified Data.Text as T
 
@@ -77,6 +83,10 @@
 import Database.MongoDB.Internal.Util (MonadIO', loop, liftIOE, true1, (<.>))
 import qualified Database.MongoDB.Internal.Protocol as P
 
+#if !MIN_VERSION_base(4,6,0)
+--mkWeakMVar = addMVarFinalizer
+#endif
+
 -- * Monad
 
 newtype Action m a = Action {unAction :: ErrorT Failure (ReaderT Context m) a}
@@ -508,8 +518,11 @@
 newCursor db col batchSize dBatch = do
 	var <- newMVar dBatch
 	let cursor = Cursor (db <.> col) batchSize var
-	addMVarFinalizer var (closeCursor cursor)
+	mkWeakMVar var (closeCursor cursor)
 	return cursor
+#if !MIN_VERSION_base(4,6,0)
+  where mkWeakMVar = addMVarFinalizer
+#endif
 
 nextBatch :: (MonadIO m, MonadBaseControl IO m) => Cursor -> Action m [Document]
 -- ^ Return next batch of documents in query result, which will be empty if finished.
@@ -694,7 +707,7 @@
 -- ^ @runCommand1 foo = runCommand [foo =: 1]@
 runCommand1 c = runCommand [c =: (1 :: Int)]
 
-eval :: (MonadIO' m) => Javascript -> Action m Document
+eval :: (MonadIO' m, Val v) => Javascript -> Action m v
 -- ^ Run code on server
 eval code = at "retval" <$> runCommand ["$eval" =: code]
 
diff --git a/System/IO/Pipeline.hs b/System/IO/Pipeline.hs
--- a/System/IO/Pipeline.hs
+++ b/System/IO/Pipeline.hs
@@ -3,6 +3,7 @@
 A pipeline closes itself when a read or write causes an error, so you can detect a broken pipeline by checking isClosed.  It also closes itself when garbage collected, or you can close it explicitly. -}
 
 {-# LANGUAGE DoRec, RecordWildCards, NamedFieldPuns, ScopedTypeVariables #-}
+{-# LANGUAGE CPP #-}
 
 module System.IO.Pipeline (
 	IOE,
@@ -19,10 +20,20 @@
 import GHC.Conc (ThreadStatus(..), threadStatus)
 
 import Control.Monad.Trans (liftIO)
+#if MIN_VERSION_base(4,6,0)
 import Control.Concurrent.MVar.Lifted (MVar, newEmptyMVar, newMVar, withMVar,
-                                       putMVar, readMVar, addMVarFinalizer)
+                                       putMVar, readMVar, mkWeakMVar)
+#else
+import Control.Concurrent.MVar.Lifted (MVar, newEmptyMVar, newMVar, withMVar,
+                                         putMVar, readMVar, addMVarFinalizer)
+#endif
 import Control.Monad.Error (ErrorT(ErrorT), runErrorT)
 
+#if !MIN_VERSION_base(4,6,0)
+mkWeakMVar :: MVar a -> IO () -> IO ()
+mkWeakMVar = addMVarFinalizer
+#endif
+
 onException :: (Monad m) => ErrorT e m a -> m () -> ErrorT e m a
 -- ^ If first action throws an exception then run second action then re-throw
 onException (ErrorT action) releaser = ErrorT $ do
@@ -58,7 +69,7 @@
 	rec
 		let pipe = Pipeline{..}
 		listenThread <- forkIO (listen pipe)
-	addMVarFinalizer vStream $ do
+	mkWeakMVar vStream $ do
 		killThread listenThread
 		closeStream stream
 	return pipe
diff --git a/mongoDB.cabal b/mongoDB.cabal
--- a/mongoDB.cabal
+++ b/mongoDB.cabal
@@ -1,5 +1,5 @@
 Name:           mongoDB
-Version:        1.3.0
+Version:        1.3.1
 Synopsis:       Driver (client) for MongoDB, a free, scalable, fast, document
                 DBMS
 Description:    This package lets you connect to MongoDB servers and