diff --git a/snaplet-postgresql-simple.cabal b/snaplet-postgresql-simple.cabal
--- a/snaplet-postgresql-simple.cabal
+++ b/snaplet-postgresql-simple.cabal
@@ -1,5 +1,5 @@
 name:           snaplet-postgresql-simple
-version:        1.1.0.0
+version:        1.2.0.0
 synopsis:       postgresql-simple snaplet for the Snap Framework
 description:    This snaplet contains support for using the Postgresql
                 database with a Snap Framework application via the
@@ -17,9 +17,10 @@
 tested-with:
   GHC == 7.8.4,
   GHC == 7.10.3,
-  GHC == 8.0.1,
-  GHC == 8.2.1,
-  GHC == 8.4.1
+  GHC == 8.0.2,
+  GHC == 8.2.2,
+  GHC == 8.4.3,
+  GHC == 8.6.4
 
 extra-source-files:
   LICENSE
@@ -50,15 +51,15 @@
     Paths_snaplet_postgresql_simple
 
   build-depends:
-    base                       >= 4       && < 4.12,
+    base                       >= 4       && < 4.13,
     bytestring                 >= 0.9.1   && < 0.11,
     clientsession              >= 0.7.2   && < 0.10,
     configurator               >= 0.2     && < 0.4,
-    lens                       >= 3.7.6   && < 4.17,
+    lens                       >= 3.7.6   && < 4.18,
     lifted-base                >= 0.2     && < 0.3,
     monad-control              >= 1.0     && < 1.1,
     mtl                        >= 2       && < 2.3,
-    postgresql-simple          >= 0.3     && < 0.6,
+    postgresql-simple          >= 0.3     && < 0.7,
     resource-pool              >= 0.2     && < 0.3,
     snap                       >= 1.0     && < 1.2,
     text                       >= 0.11    && < 1.3,
diff --git a/src/Snap/Snaplet/PostgresqlSimple.hs b/src/Snap/Snaplet/PostgresqlSimple.hs
--- a/src/Snap/Snaplet/PostgresqlSimple.hs
+++ b/src/Snap/Snaplet/PostgresqlSimple.hs
@@ -98,6 +98,8 @@
   , withTransaction
   , withTransactionLevel
   , withTransactionMode
+  , withTransactionEither
+  , withTransactionModeEither
   , formatMany
   , formatQuery
 
@@ -130,7 +132,6 @@
 
   ) where
 
-import           Control.Applicative
 import qualified Control.Exception                      as E
 import           Control.Lens                           (set, (^#))
 import           Control.Monad                          (liftM)
@@ -453,6 +454,31 @@
         P.beginMode mode con
         r <- unmask (run act) `E.onException` P.rollback con
         P.commit con
+        return r
+    restoreM r
+
+------------------------------------------------------------------------------
+-- | Be careful that you do not call Snap's `finishWith` function anywhere
+-- inside the function that you pass to `withTransactionMode`.  Doing so has
+-- been known to cause DB connection leaks.
+withTransactionEither :: (HasPostgres m)
+                      => m (Either a b) -> m (Either a b)
+withTransactionEither = withTransactionModeEither P.defaultTransactionMode
+
+------------------------------------------------------------------------------
+-- | Be careful that you do not call Snap's `finishWith` function anywhere
+-- inside the function that you pass to `withTransactionMode`.  Doing so has
+-- been known to cause DB connection leaks.
+withTransactionModeEither :: (HasPostgres m)
+                          => P.TransactionMode -> m (Either a b) -> m (Either a b)
+withTransactionModeEither mode act = withPG $ do
+    pg <- getPostgresState
+    r <- liftBaseWith $ \run -> E.mask
+                      $ \unmask -> withConnection pg
+                      $ \con -> do
+        P.beginMode mode con
+        r <- unmask (run act) `E.onException` P.rollback con
+        either (const $ P.rollback con) (const $ P.commit con) $ restoreM r
         return r
     restoreM r
 
diff --git a/src/Snap/Snaplet/PostgresqlSimple/Internal.hs b/src/Snap/Snaplet/PostgresqlSimple/Internal.hs
--- a/src/Snap/Snaplet/PostgresqlSimple/Internal.hs
+++ b/src/Snap/Snaplet/PostgresqlSimple/Internal.hs
@@ -10,7 +10,6 @@
 import           Control.Monad.Trans.Control       (MonadBaseControl (..),
                                                     control)
 import           Control.Monad.Trans.Identity      (IdentityT (IdentityT))
-import           Control.Monad.Trans.List          (ListT (ListT))
 import           Control.Monad.Trans.Maybe         (MaybeT (MaybeT))
 import           Control.Monad.Trans.Reader        (ReaderT (ReaderT))
 import qualified Control.Monad.Trans.RWS.Lazy      as LRWS
@@ -45,12 +44,6 @@
 instance HasPostgres m => HasPostgres (IdentityT m) where
     getPostgresState = lift getPostgresState
     setLocalPostgresState pg (IdentityT m) = IdentityT $
-      setLocalPostgresState pg m
-
-
-instance HasPostgres m => HasPostgres (ListT m) where
-    getPostgresState = lift getPostgresState
-    setLocalPostgresState pg (ListT m) = ListT $
       setLocalPostgresState pg m