diff --git a/hasql.cabal b/hasql.cabal
--- a/hasql.cabal
+++ b/hasql.cabal
@@ -1,5 +1,5 @@
 name: hasql
-version: 1.4.2
+version: 1.4.3
 category: Hasql, Database, PostgreSQL
 synopsis: An efficient PostgreSQL driver with a flexible mapping API
 description:
diff --git a/library/Hasql/Private/Decoders.hs b/library/Hasql/Private/Decoders.hs
--- a/library/Hasql/Private/Decoders.hs
+++ b/library/Hasql/Private/Decoders.hs
@@ -113,7 +113,7 @@
 @
 -}
 newtype Row a = Row (Row.Row a)
-  deriving (Functor, Applicative, Monad)
+  deriving (Functor, Applicative, Monad, MonadFail)
 
 {-|
 Lift an individual non-nullable value decoder to a composable row decoder.
@@ -268,7 +268,7 @@
 {-|
 Decoder of the @TIMETZ@ values.
 
-Unlike in case of @TIMESTAMPTZ@, 
+Unlike in case of @TIMESTAMPTZ@,
 Postgres does store the timezone information for @TIMETZ@.
 However the Haskell's \"time\" library does not contain any composite type,
 that fits the task, so we use a pair of 'TimeOfDay' and 'TimeZone'
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
@@ -69,10 +69,10 @@
 serverError =
   Result $ ReaderT $ \(_, result) -> ExceptT $ do
     code <- 
-      fmap (fromMaybe ($bug "No code")) $
+      fmap fold $
       LibPQ.resultErrorField result LibPQ.DiagSqlstate
     message <- 
-      fmap (fromMaybe ($bug "No message")) $
+      fmap fold $
       LibPQ.resultErrorField result LibPQ.DiagMessagePrimary
     detail <- 
       LibPQ.resultErrorField result LibPQ.DiagMessageDetail
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
@@ -3,14 +3,19 @@
 import Hasql.Private.Prelude hiding (error)
 import Hasql.Private.Errors
 import qualified Database.PostgreSQL.LibPQ as LibPQ
+import qualified Data.Text as T
 import qualified PostgreSQL.Binary.Decoding as A
 import qualified Hasql.Private.Decoders.Value as Value
+import Control.Monad.Fail (MonadFail(..))
 
 
 newtype Row a =
   Row (ReaderT Env (ExceptT RowError IO) a)
   deriving (Functor, Applicative, Monad)
 
+instance MonadFail Row where
+  fail = error . ValueError . T.pack
+
 data Env =
   Env !LibPQ.Result !LibPQ.Row !LibPQ.Column !Bool !(IORef LibPQ.Column)
 
@@ -35,14 +40,14 @@
 {-# INLINE value #-}
 value :: Value.Value a -> Row (Maybe a)
 value valueDec =
-  {-# SCC "value" #-} 
+  {-# SCC "value" #-}
   Row $ ReaderT $ \(Env result row columnsAmount integerDatetimes columnRef) -> ExceptT $ do
     col <- readIORef columnRef
     writeIORef columnRef (succ col)
     if col < columnsAmount
       then do
         valueMaybe <- {-# SCC "getvalue'" #-} LibPQ.getvalue' result row col
-        pure $ 
+        pure $
           case valueMaybe of
             Nothing ->
               Right Nothing
@@ -56,5 +61,5 @@
 {-# INLINE nonNullValue #-}
 nonNullValue :: Value.Value a -> Row a
 nonNullValue valueDec =
-  {-# SCC "nonNullValue" #-} 
+  {-# SCC "nonNullValue" #-}
   value valueDec >>= maybe (error UnexpectedNull) pure
diff --git a/tasty/Main/Prelude.hs b/tasty/Main/Prelude.hs
--- a/tasty/Main/Prelude.hs
+++ b/tasty/Main/Prelude.hs
@@ -1,7 +1,6 @@
 module Main.Prelude
 (
   module Exports,
-  mapLeft,
 )
 where
 
@@ -9,8 +8,3 @@
 -- rerebase
 -------------------------
 import Prelude as Exports
-
-{-# INLINE mapLeft #-}
-mapLeft :: (a -> c) -> Either a b -> Either c b
-mapLeft f =
-  either (Left . f) Right