diff --git a/hasql.cabal b/hasql.cabal
--- a/hasql.cabal
+++ b/hasql.cabal
@@ -1,7 +1,7 @@
 name:
   hasql
 version:
-  1.1
+  1.1.1
 category:
   Hasql, Database, PostgreSQL
 synopsis:
@@ -93,7 +93,6 @@
     profunctors >= 5.1 && < 6,
     contravariant-extras == 0.3.*,
     contravariant >= 1.3 && < 2,
-    either >= 4.4.1 && < 5,
     mtl >= 2 && < 3,
     transformers >= 0.3 && < 0.6,
     -- errors:
@@ -124,12 +123,11 @@
     -- database:
     hasql,
     -- testing:
-    tasty == 0.11.*,
-    tasty-quickcheck == 0.8.*,
-    tasty-smallcheck == 0.8.*,
-    tasty-hunit == 0.9.*,
+    tasty >= 0.12 && < 0.13,
+    tasty-quickcheck >= 0.9 && < 0.10,
+    tasty-hunit >= 0.9 && < 0.10,
     quickcheck-instances >= 0.3.11 && < 0.4,
-    QuickCheck >= 2.8.1 && < 2.10,
+    QuickCheck >= 2.8.1 && < 3,
     -- general:
     data-default-class,
     -- 
diff --git a/library/Hasql/Private/Connection.hs b/library/Hasql/Private/Connection.hs
--- a/library/Hasql/Private/Connection.hs
+++ b/library/Hasql/Private/Connection.hs
@@ -25,9 +25,9 @@
 acquire :: Settings.Settings -> IO (Either ConnectionError Connection)
 acquire settings =
   {-# SCC "acquire" #-}
-  runEitherT $ do
+  runExceptT $ do
     pqConnection <- lift (IO.acquireConnection settings)
-    lift (IO.checkConnectionStatus pqConnection) >>= traverse left
+    lift (IO.checkConnectionStatus pqConnection) >>= traverse throwError
     lift (IO.initConnection pqConnection)
     integerDatetimes <- lift (IO.getIntegerDatetimes pqConnection)
     registry <- lift (IO.acquirePreparedStatementRegistry)
diff --git a/library/Hasql/Private/Decoders/Result.hs b/library/Hasql/Private/Decoders/Result.hs
--- a/library/Hasql/Private/Decoders/Result.hs
+++ b/library/Hasql/Private/Decoders/Result.hs
@@ -11,7 +11,7 @@
 
 
 newtype Result a =
-  Result (ReaderT (Bool, LibPQ.Result) (EitherT Error IO) a)
+  Result (ReaderT (Bool, LibPQ.Result) (ExceptT Error IO) a)
   deriving (Functor, Applicative, Monad)
 
 data Error =
@@ -48,7 +48,7 @@
 {-# INLINE run #-}
 run :: Result a -> (Bool, LibPQ.Result) -> IO (Either Error a)
 run (Result reader) env =
-  runEitherT (runReaderT reader env)
+  runExceptT (runReaderT reader env)
 
 {-# INLINE unit #-}
 unit :: Result ()
@@ -65,7 +65,7 @@
     checkExecStatus $ \case
       LibPQ.CommandOk -> True
       _ -> False
-    Result $ ReaderT $ \(_, result) -> EitherT $
+    Result $ ReaderT $ \(_, result) -> ExceptT $
       LibPQ.cmdTuples result & fmap cmdTuplesReader
   where
     cmdTuplesReader =
@@ -92,12 +92,12 @@
         LibPQ.BadResponse   -> serverError
         LibPQ.NonfatalError -> serverError
         LibPQ.FatalError    -> serverError
-        _ -> Result $ lift $ EitherT $ pure $ Left $ UnexpectedResult $ "Unexpected result status: " <> (fromString $ show status)
+        _ -> Result $ lift $ ExceptT $ pure $ Left $ UnexpectedResult $ "Unexpected result status: " <> (fromString $ show status)
 
 {-# INLINE serverError #-}
 serverError :: Result ()
 serverError =
-  Result $ ReaderT $ \(_, result) -> EitherT $ do
+  Result $ ReaderT $ \(_, result) -> ExceptT $ do
     code <- 
       fmap (fromMaybe ($bug "No code")) $
       LibPQ.resultErrorField result LibPQ.DiagSqlstate
@@ -117,7 +117,7 @@
     checkExecStatus $ \case
       LibPQ.TuplesOk -> True
       _ -> False
-    Result $ ReaderT $ \(integerDatetimes, result) -> EitherT $ do
+    Result $ ReaderT $ \(integerDatetimes, result) -> ExceptT $ do
       maxRows <- LibPQ.ntuples result
       case maxRows of
         0 -> return (Right Nothing)
@@ -138,7 +138,7 @@
     checkExecStatus $ \case
       LibPQ.TuplesOk -> True
       _ -> False
-    Result $ ReaderT $ \(integerDatetimes, result) -> EitherT $ do
+    Result $ ReaderT $ \(integerDatetimes, result) -> ExceptT $ do
       maxRows <- LibPQ.ntuples result
       case maxRows of
         1 -> do
@@ -158,7 +158,7 @@
     checkExecStatus $ \case
       LibPQ.TuplesOk -> True
       _ -> False
-    Result $ ReaderT $ \(integerDatetimes, result) -> EitherT $ do
+    Result $ ReaderT $ \(integerDatetimes, result) -> ExceptT $ do
       maxRows <- LibPQ.ntuples result
       maxCols <- LibPQ.nfields result
       mvector <- MutableVector.unsafeNew (rowToInt maxRows)
@@ -185,7 +185,7 @@
     checkExecStatus $ \case
       LibPQ.TuplesOk -> True
       _ -> False
-    Result $ ReaderT $ \(integerDatetimes, result) -> EitherT $ {-# SCC "traversal" #-} do
+    Result $ ReaderT $ \(integerDatetimes, result) -> ExceptT $ {-# SCC "traversal" #-} do
       maxRows <- LibPQ.ntuples result
       maxCols <- LibPQ.nfields result
       accRef <- newIORef init
@@ -212,7 +212,7 @@
     checkExecStatus $ \case
       LibPQ.TuplesOk -> True
       _ -> False
-    Result $ ReaderT $ \(integerDatetimes, result) -> EitherT $ do
+    Result $ ReaderT $ \(integerDatetimes, result) -> ExceptT $ do
       maxRows <- LibPQ.ntuples result
       maxCols <- LibPQ.nfields result
       accRef <- newIORef init
diff --git a/library/Hasql/Private/Decoders/Results.hs b/library/Hasql/Private/Decoders/Results.hs
--- a/library/Hasql/Private/Decoders/Results.hs
+++ b/library/Hasql/Private/Decoders/Results.hs
@@ -19,7 +19,7 @@
 
 
 newtype Results a =
-  Results (ReaderT (Bool, LibPQ.Connection) (EitherT Error IO) a)
+  Results (ReaderT (Bool, LibPQ.Connection) (ExceptT Error IO) a)
   deriving (Functor, Applicative, Monad)
 
 data Error =
@@ -34,12 +34,12 @@
 {-# INLINE run #-}
 run :: Results a -> (Bool, LibPQ.Connection) -> IO (Either Error a)
 run (Results stack) env =
-  runEitherT (runReaderT stack env)
+  runExceptT (runReaderT stack env)
 
 {-# INLINE clientError #-}
 clientError :: Results a
 clientError =
-  Results $ ReaderT $ \(_, connection) -> EitherT $
+  Results $ ReaderT $ \(_, connection) -> ExceptT $
   fmap (Left . ClientError) (LibPQ.errorMessage connection)
 
 -- |
@@ -47,7 +47,7 @@
 {-# INLINE single #-}
 single :: Result.Result a -> Results a
 single resultDec =
-  Results $ ReaderT $ \(integerDatetimes, connection) -> EitherT $ do
+  Results $ ReaderT $ \(integerDatetimes, connection) -> ExceptT $ do
     resultMaybe <- LibPQ.getResult connection
     case resultMaybe of
       Just result ->
@@ -60,7 +60,7 @@
 {-# INLINE getResult #-}
 getResult :: Results LibPQ.Result
 getResult =
-  Results $ ReaderT $ \(_, connection) -> EitherT $ do
+  Results $ ReaderT $ \(_, connection) -> ExceptT $ do
     resultMaybe <- LibPQ.getResult connection
     case resultMaybe of
       Just result -> pure (Right result)
@@ -88,4 +88,4 @@
           loop integerDatetimes connection <* checkErrors
           where
             checkErrors =
-              EitherT $ fmap (mapLeft ResultError) $ Result.run Result.unit (integerDatetimes, result)
+              ExceptT $ fmap (mapLeft ResultError) $ Result.run Result.unit (integerDatetimes, result)
diff --git a/library/Hasql/Private/Decoders/Row.hs b/library/Hasql/Private/Decoders/Row.hs
--- a/library/Hasql/Private/Decoders/Row.hs
+++ b/library/Hasql/Private/Decoders/Row.hs
@@ -7,7 +7,7 @@
 
 
 newtype Row a =
-  Row (ReaderT Env (EitherT Error IO) a)
+  Row (ReaderT Env (ExceptT Error IO) a)
   deriving (Functor, Applicative, Monad)
 
 data Env =
@@ -28,12 +28,12 @@
 run (Row impl) (result, row, columnsAmount, integerDatetimes) =
   do
     columnRef <- newIORef 0
-    runEitherT (runReaderT impl (Env result row columnsAmount integerDatetimes columnRef))
+    runExceptT (runReaderT impl (Env result row columnsAmount integerDatetimes columnRef))
 
 {-# INLINE error #-}
 error :: Error -> Row a
 error x =
-  Row (ReaderT (const (EitherT (pure (Left x)))))
+  Row (ReaderT (const (ExceptT (pure (Left x)))))
 
 -- |
 -- Next value, decoded using the provided value decoder.
@@ -41,7 +41,7 @@
 value :: Value.Value a -> Row (Maybe a)
 value valueDec =
   {-# SCC "value" #-} 
-  Row $ ReaderT $ \(Env result row columnsAmount integerDatetimes columnRef) -> EitherT $ do
+  Row $ ReaderT $ \(Env result row columnsAmount integerDatetimes columnRef) -> ExceptT $ do
     col <- readIORef columnRef
     writeIORef columnRef (succ col)
     if col < columnsAmount
diff --git a/library/Hasql/Private/IO.hs b/library/Hasql/Private/IO.hs
--- a/library/Hasql/Private/IO.hs
+++ b/library/Hasql/Private/IO.hs
@@ -114,9 +114,9 @@
   [Maybe (ByteString, LibPQ.Format)] ->
   IO (Either ResultsDecoders.Error ())
 sendPreparedParametricQuery connection registry template oidList valueAndFormatList =
-  runEitherT $ do
-    key <- EitherT $ getPreparedStatementKey connection registry template oidList
-    EitherT $ checkedSend connection $ LibPQ.sendQueryPrepared connection key valueAndFormatList LibPQ.Binary
+  runExceptT $ do
+    key <- ExceptT $ getPreparedStatementKey connection registry template oidList
+    ExceptT $ checkedSend connection $ LibPQ.sendQueryPrepared connection key valueAndFormatList LibPQ.Binary
 
 {-# INLINE sendUnpreparedParametricQuery #-}
 sendUnpreparedParametricQuery ::
diff --git a/library/Hasql/Private/Prelude.hs b/library/Hasql/Private/Prelude.hs
--- a/library/Hasql/Private/Prelude.hs
+++ b/library/Hasql/Private/Prelude.hs
@@ -10,6 +10,7 @@
   forMToZero_,
   forMFromZero_,
   strictCons,
+  mapLeft,
 )
 where
 
@@ -22,9 +23,13 @@
 -------------------------
 import Control.Monad.IO.Class as Exports
 import Control.Monad.Trans.Class as Exports
-import Control.Monad.Trans.Maybe as Exports hiding (liftListen, liftPass)
-import Control.Monad.Trans.Reader as Exports hiding (liftCallCC, liftCatch)
-import Control.Monad.Trans.State.Strict as Exports hiding (liftCallCC, liftCatch, liftListen, liftPass)
+import Control.Monad.Trans.Cont as Exports hiding (shift, callCC)
+import Control.Monad.Trans.Except as Exports (ExceptT(ExceptT), Except, except, runExcept, runExceptT, mapExcept, mapExceptT, withExcept, withExceptT, throwE, catchE)
+import Control.Monad.Trans.Maybe as Exports
+import Control.Monad.Trans.Reader as Exports (Reader, runReader, mapReader, withReader, ReaderT(ReaderT), runReaderT, mapReaderT, withReaderT)
+import Control.Monad.Trans.State.Strict as Exports (State, runState, evalState, execState, mapState, withState, StateT(StateT), runStateT, evalStateT, execStateT, mapStateT, withStateT)
+import Control.Monad.Trans.Writer.Strict as Exports (Writer, runWriter, execWriter, mapWriter, WriterT(..), execWriterT, mapWriterT)
+import Data.Functor.Compose as Exports
 import Data.Functor.Identity as Exports
 
 -- mtl
@@ -48,11 +53,6 @@
 -------------------------
 import Contravariant.Extras as Exports
 
--- either
--------------------------
-import Control.Monad.Trans.Either as Exports
-import Data.Either.Combinators as Exports
-
 -- semigroups
 -------------------------
 import Data.Semigroup as Exports
@@ -128,3 +128,8 @@
 strictCons :: a -> [a] -> [a]
 strictCons !a b =
   let !c = a : b in c
+
+{-# INLINE mapLeft #-}
+mapLeft :: (a -> c) -> Either a b -> Either c b
+mapLeft f =
+  either (Left . f) Right
diff --git a/library/Hasql/Private/Query.hs b/library/Hasql/Private/Query.hs
--- a/library/Hasql/Private/Query.hs
+++ b/library/Hasql/Private/Query.hs
@@ -34,7 +34,7 @@
 --       else insert -< params
 -- @
 newtype Query a b =
-  Query (Kleisli (ReaderT Connection.Connection (EitherT Decoders.Results.Error IO)) a b)
+  Query (Kleisli (ReaderT Connection.Connection (ExceptT Decoders.Results.Error IO)) a b)
   deriving (Category, Arrow, ArrowChoice, ArrowLoop, ArrowApply)
 
 instance Functor (Query a) where
@@ -54,7 +54,7 @@
 statement template encoder decoder preparable =
   Query $ Kleisli $ \params -> 
     ReaderT $ \(Connection.Connection pqConnectionRef integerDatetimes registry) -> 
-      EitherT $ withMVar pqConnectionRef $ \pqConnection -> do
+      ExceptT $ withMVar pqConnectionRef $ \pqConnection -> do
         r1 <- IO.sendParametricQuery pqConnection integerDatetimes registry template encoder preparable params
         r2 <- IO.getResults pqConnection integerDatetimes decoder
         return $ r1 *> r2
diff --git a/library/Hasql/Private/Session.hs b/library/Hasql/Private/Session.hs
--- a/library/Hasql/Private/Session.hs
+++ b/library/Hasql/Private/Session.hs
@@ -14,14 +14,14 @@
 -- |
 -- A batch of actions to be executed in the context of a database connection.
 newtype Session a =
-  Session (ReaderT Connection.Connection (EitherT Error IO) a)
+  Session (ReaderT Connection.Connection (ExceptT Error IO) a)
   deriving (Functor, Applicative, Monad, MonadError Error, MonadIO)
 
 -- |
 -- Executes a bunch of commands on the provided connection.
 run :: Session a -> Connection.Connection -> IO (Either Error a)
 run (Session impl) connection =
-  runEitherT $
+  runExceptT $
   runReaderT impl connection
 
 -- |
@@ -31,7 +31,7 @@
 sql :: ByteString -> Session ()
 sql sql =
   Session $ ReaderT $ \(Connection.Connection pqConnectionRef integerDatetimes registry) ->
-    EitherT $ fmap (mapLeft unsafeCoerce) $ withMVar pqConnectionRef $ \pqConnection -> do
+    ExceptT $ fmap (mapLeft unsafeCoerce) $ withMVar pqConnectionRef $ \pqConnection -> do
       r1 <- IO.sendNonparametricQuery pqConnection sql
       r2 <- IO.getResults pqConnection integerDatetimes decoder
       return $ r1 *> r2
diff --git a/tasty/Main/Connection.hs b/tasty/Main/Connection.hs
--- a/tasty/Main/Connection.hs
+++ b/tasty/Main/Connection.hs
@@ -9,10 +9,10 @@
 
 with :: (HC.Connection -> IO a) -> IO (Either HC.ConnectionError a)
 with handler =
-  runEitherT $ acquire >>= \connection -> use connection <* release connection
+  runExceptT $ acquire >>= \connection -> use connection <* release connection
   where
     acquire =
-      EitherT $ HC.acquire settings
+      ExceptT $ HC.acquire settings
       where
         settings =
           HC.settings host port user password database
diff --git a/tasty/Main/DSL.hs b/tasty/Main/DSL.hs
--- a/tasty/Main/DSL.hs
+++ b/tasty/Main/DSL.hs
@@ -26,10 +26,10 @@
 
 session :: Session a -> IO (Either SessionError a)
 session session =
-  runEitherT $ acquire >>= \connection -> use connection <* release connection
+  runExceptT $ acquire >>= \connection -> use connection <* release connection
   where
     acquire =
-      EitherT $ fmap (mapLeft ConnectionError) $ HC.acquire settings
+      ExceptT $ fmap (mapLeft ConnectionError) $ HC.acquire settings
       where
         settings =
           HC.settings host port user password database
@@ -40,7 +40,7 @@
             password = ""
             database = "postgres"
     use connection =
-      EitherT $
+      ExceptT $
       fmap (mapLeft SessionError) $
       Hasql.Session.run session connection
     release connection =