diff --git a/hasql-postgres.cabal b/hasql-postgres.cabal
--- a/hasql-postgres.cabal
+++ b/hasql-postgres.cabal
@@ -1,7 +1,7 @@
 name:
   hasql-postgres
 version:
-  0.3.3
+  0.4.0
 synopsis:
   A "PostgreSQL" backend for the "hasql" library
 description:
@@ -84,12 +84,13 @@
     bytestring >= 0.10.4.0 && < 0.11,
     hashable == 1.2.*,
     -- control:
+    either == 4.*,
     list-t >= 0.2.3 && < 0.3,
     -- errors:
     loch-th == 0.2.*,
     placeholders == 0.1.*,
     -- general:
-    mtl-prelude == 2.0.*,
+    mtl-prelude < 3,
     base-prelude >= 0.1.3 && < 0.2,
     base >= 4.5 && < 4.8
 
@@ -134,12 +135,13 @@
     bytestring >= 0.10.4.0 && < 0.11,
     hashable == 1.2.*,
     -- control:
+    either == 4.*,
     list-t >= 0.2.3 && < 0.3,
     -- errors:
     loch-th == 0.2.*,
     placeholders == 0.1.*,
     -- general:
-    mtl-prelude == 2.0.*,
+    mtl-prelude < 3,
     base-prelude >= 0.1.3 && < 0.2,
     base >= 4.5 && < 4.8
 
@@ -181,7 +183,7 @@
     hashable == 1.2.*,
     -- general:
     list-t == 0.2.*,
-    mtl-prelude == 2.0.*,
+    mtl-prelude < 3,
     base-prelude >= 0.1.3 && < 0.2,
     base >= 4.5 && < 4.8
 
diff --git a/library/Hasql/Postgres.hs b/library/Hasql/Postgres.hs
--- a/library/Hasql/Postgres.hs
+++ b/library/Hasql/Postgres.hs
@@ -59,7 +59,7 @@
     }
   connect p =
     do
-      r <- runExceptT $ Connector.open settings
+      r <- runEitherT $ Connector.open settings
       c <- either (\e -> throwIO $ Backend.CantConnect $ fromString $ show e) return r
       Connection <$> pure c <*> StatementPreparer.new c <*> newIORef Nothing <*> getIntegerDatetimes c
     where
diff --git a/library/Hasql/Postgres/Connector.hs b/library/Hasql/Postgres/Connector.hs
--- a/library/Hasql/Postgres/Connector.hs
+++ b/library/Hasql/Postgres/Connector.hs
@@ -1,9 +1,7 @@
--- |
--- Mid-level abstractions over gritty details of \"lib-pq\".
 module Hasql.Postgres.Connector where
 
 import Hasql.Postgres.Prelude hiding (Error)
-import qualified Database.PostgreSQL.LibPQ as L
+import qualified Database.PostgreSQL.LibPQ as PQ
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Builder as BB
 import qualified Data.ByteString.Lazy as BL
@@ -35,20 +33,20 @@
 
 -- |
 -- Establish and initialize a connection.
-open :: Settings -> ExceptT Error IO L.Connection
+open :: Settings -> EitherT Error IO PQ.Connection
 open s =
   do
-    c <- lift $ L.connectdb (settingsBS s)
+    c <- lift $ PQ.connectdb (settingsBS s)
     do
-      s <- lift $ L.status c
-      when (s /= L.ConnectionOk) $ 
+      s <- lift $ PQ.status c
+      when (s /= PQ.ConnectionOk) $ 
         do
-          m <- lift $ L.errorMessage c
-          throwError $ BadStatus m
+          m <- lift $ PQ.errorMessage c
+          left $ BadStatus m
     do
-      v <- lift $ L.serverVersion c
-      when (v < 80200) $ throwError $ UnsupportedVersion v
-    lift $ L.exec c $ mconcat $ map (<> ";") $ 
+      v <- lift $ PQ.serverVersion c
+      when (v < 80200) $ left $ UnsupportedVersion v
+    lift $ PQ.exec c $ mconcat $ map (<> ";") $ 
       [ 
         "SET client_encoding = 'UTF8'",
         "SET client_min_messages TO WARNING"
diff --git a/library/Hasql/Postgres/Prelude.hs b/library/Hasql/Postgres/Prelude.hs
--- a/library/Hasql/Postgres/Prelude.hs
+++ b/library/Hasql/Postgres/Prelude.hs
@@ -12,11 +12,15 @@
 
 -- base-prelude
 -------------------------
-import BasePrelude as Exports hiding (assert)
+import BasePrelude as Exports hiding (assert, left, right)
 
 -- mtl-prelude
 -------------------------
 import MTLPrelude as Exports hiding (shift)
+
+-- either
+-------------------------
+import Control.Monad.Trans.Either as Exports
 
 -- list-t
 -------------------------
diff --git a/library/Hasql/Postgres/TemplateConverter/Parser.hs b/library/Hasql/Postgres/TemplateConverter/Parser.hs
--- a/library/Hasql/Postgres/TemplateConverter/Parser.hs
+++ b/library/Hasql/Postgres/TemplateConverter/Parser.hs
@@ -12,7 +12,7 @@
 
 run :: ByteString -> Parser a -> Either Text a
 run input parser =
-  left fromString $ parseOnly (parser <* endOfInput) input
+  either (Left . fromString) Right $ parseOnly (parser <* endOfInput) input
 
 parts :: Parser [Part]
 parts =