diff --git a/src/Database/Esqueleto.hs b/src/Database/Esqueleto.hs
index 773fec1..d082191 100644
--- a/src/Database/Esqueleto.hs
+++ b/src/Database/Esqueleto.hs
@@ -100,7 +100,6 @@ module Database.Esqueleto
     -- * Helpers
   , valkey
   , valJ
-  , EsqueletoUpsert(..)
 
     -- * Re-exports
     -- $reexports
diff --git a/src/Database/Esqueleto/Internal/Internal.hs b/src/Database/Esqueleto/Internal/Internal.hs
index 8db442f..88ce078 100644
--- a/src/Database/Esqueleto/Internal/Internal.hs
+++ b/src/Database/Esqueleto/Internal/Internal.hs
@@ -56,9 +56,6 @@ import qualified Data.Text.Lazy.Builder as TLB
 
 import Data.Typeable (Typeable)
 import Text.Blaze.Html (Html)
-import Database.Persist.Class (OnlyOneUniqueKey)
-import Control.Monad.Reader (ReaderT)
-import Data.List.NonEmpty( NonEmpty( (:|) ) )
 
 -- | (Internal) Start a 'from' query with an entity. 'from'
 -- does two kinds of magic using 'fromStart', 'fromJoin' and
@@ -1266,6 +1263,7 @@ data UnexpectedCaseError =
   | InsertionFinalError
   | NewIdentForError
   | UnsafeSqlCaseError
+  | OperationNotSupported
   deriving (Show)
 
 data SqlBinOpCompositeError =
@@ -2885,88 +2883,4 @@ insertSelect = void . insertSelectCount
 -- | Insert a 'PersistField' for every selected value, return the count afterward
 insertSelectCount :: (MonadIO m, PersistEntity a) =>
   SqlQuery (SqlExpr (Insertion a)) -> SqlWriteT m Int64
-insertSelectCount = rawEsqueleto INSERT_INTO . fmap EInsertFinal
-
--- | A class for allowing the use of upsert operation using
--- esqueleto's types.
-class (PersistUniqueWrite backend,
-        PersistQueryWrite backend,
-        IsPersistBackend (BaseBackend backend),
-        BackendCompatible SqlBackend backend,
-        BackendCompatible SqlBackend (BaseBackend backend)) =>
-      EsqueletoUpsert backend  where
-    upsert
-        :: (MonadIO m, PersistRecordBackend record backend, OnlyOneUniqueKey record)
-        => record
-        -- ^ new record to insert
-        -> [SqlExpr (Update record)]
-        -- ^ updates to perform if the record already exists
-        -> ReaderT backend m (Entity record)
-        -- ^ the record in the database after the operation
-    upsert record updates = do
-        uniqueKey <- onlyUnique record
-        upsertBy uniqueKey record updates
-
-    upsertBy :: (MonadIO m, PersistRecordBackend record backend)
-        => Unique record
-        -- ^ uniqueness constraint to find by
-        -> record
-        -- ^ new record to insert
-        -> [SqlExpr (Update record)]
-        -- ^ updates to perform if the record already exists
-        -> ReaderT backend m (Entity record)
-        -- ^ the record in the database after the operation
-    upsertBy = defaultUpsert
-
-defaultUpsert
-    :: (MonadIO m, PersistRecordBackend record backend,
-        PersistQueryWrite backend,
-        PersistUniqueWrite backend,
-        IsPersistBackend (BaseBackend backend),
-        BackendCompatible SqlBackend backend,
-        BackendCompatible SqlBackend (BaseBackend backend))
-    => Unique record
-    -> record
-    -> [SqlExpr (Update record)]
-    -> ReaderT backend m (Entity record)
-defaultUpsert uniqueKey record updates = do
-    mrecord <- getBy uniqueKey
-    maybe (insertEntity record) updateGetEntity mrecord
-  where
-    updateGetEntity (Entity k _) = fmap head $ do
-      update $ \r -> do
-        set r updates
-        where_ (r ^. persistIdField ==. val k)
-      select $ from $ \r -> do
-        where_ (r ^. persistIdField ==. val k)
-        return r
-
--- Currently only postgres implements connUpsertSql, check that '?' are
--- added in the same order as postgres when adding connUpsertSql to another
--- backend.
-instance EsqueletoUpsert SqlBackend where
-  upsertBy uniqueKey record updates = do
-    sqlB <- R.ask
-    maybe
-      (defaultUpsert uniqueKey record updates)
-      (handler sqlB)
-      (connUpsertSql sqlB)
-    where
-      addVals l = map toPersistValue (toPersistFields record) ++ l ++ persistUniqueToValues uniqueKey
-      entDef = entityDef (Just record)
-      uDef = head $ filter ((==) (persistUniqueToFieldNames uniqueKey) . uniqueFields) $ entityUniques entDef
-      updatesText conn = first builderToText $ renderUpdates conn updates
-      handler conn f = fmap head $ uncurry rawSql $
-        (***) (f entDef (uDef :| [])) addVals $ updatesText conn
-
--- | Renders a [SqlExpr (Update val)] into a (TLB.Builder, [PersistValue]) with a given backend.
-renderUpdates :: BackendCompatible SqlBackend backend =>
-    backend
-    -> [SqlExpr (Update val)]
-    -> (TLB.Builder, [PersistValue])
-renderUpdates conn = uncommas' . concatMap renderUpdate
-    where
-      mk (ERaw _ f)        = [f info]
-      mk (ECompositeKey _) = throw (CompositeKeyErr MakeSetError) -- FIXME
-      renderUpdate (ESet f) = mk (f undefined) -- second parameter of f is always unused
-      info = (projectBackend conn, initialIdentState)
\ No newline at end of file
+insertSelectCount = rawEsqueleto INSERT_INTO . fmap EInsertFinal
\ No newline at end of file
diff --git a/src/Database/Esqueleto/Internal/PersistentImport.hs b/src/Database/Esqueleto/Internal/PersistentImport.hs
index 43725b0..638d538 100644
--- a/src/Database/Esqueleto/Internal/PersistentImport.hs
+++ b/src/Database/Esqueleto/Internal/PersistentImport.hs
@@ -147,4 +147,4 @@ import Database.Persist.Sql hiding
   , selectKeysList, deleteCascadeWhere, (=.), (+=.), (-=.), (*=.), (/=.)
   , (==.), (!=.), (<.), (>.), (<=.), (>=.), (<-.), (/<-.), (||.)
   , listToJSON, mapToJSON, getPersistMap, limitOffsetOrder, selectSource
-  , update , count , upsertBy, upsert)
+  , update , count)
diff --git a/src/Database/Esqueleto/Internal/Sql.hs b/src/Database/Esqueleto/Internal/Sql.hs
index e50e6e4..7818624 100644
--- a/src/Database/Esqueleto/Internal/Sql.hs
+++ b/src/Database/Esqueleto/Internal/Sql.hs
@@ -71,7 +71,6 @@ module Database.Esqueleto.Internal.Sql
   , parens
   , toArgList
   , builderToText
-  , EsqueletoUpsert(..)
   ) where
 
 import Database.Esqueleto.Internal.Internal
diff --git a/src/Database/Esqueleto/PostgreSQL.hs b/src/Database/Esqueleto/PostgreSQL.hs
index b89cac7..f9254dd 100644
--- a/src/Database/Esqueleto/PostgreSQL.hs
+++ b/src/Database/Esqueleto/PostgreSQL.hs
@@ -18,6 +18,8 @@ module Database.Esqueleto.PostgreSQL
   , chr
   , now_
   , random_
+  , upsert
+  , upsertBy
   -- * Internal
   , unsafeSqlAggregateFunction
   ) where
@@ -28,8 +30,17 @@ import           Data.Semigroup
 import qualified Data.Text.Internal.Builder                   as TLB
 import           Data.Time.Clock                              (UTCTime)
 import           Database.Esqueleto.Internal.Language         hiding (random_)
-import           Database.Esqueleto.Internal.PersistentImport
+import           Database.Esqueleto.Internal.PersistentImport hiding (upsert, upsertBy)
 import           Database.Esqueleto.Internal.Sql
+import           Database.Esqueleto.Internal.Internal         (EsqueletoError(..), CompositeKeyError(..), 
+                                                              UnexpectedCaseError(..))
+import           Database.Persist.Class                       (OnlyOneUniqueKey)
+import           Data.List.NonEmpty                           ( NonEmpty( (:|) ) )
+import           Control.Arrow                                ((***), first)
+import           Control.Exception                            (Exception, throw, throwIO)
+import           Control.Monad.IO.Class                       (MonadIO (..))
+import qualified Control.Monad.Trans.Reader                   as R
+
 
 -- | (@random()@) Split out into database specific modules
 -- because MySQL uses `rand()`.
@@ -152,3 +163,52 @@ chr = unsafeSqlFunction "chr"
 
 now_ :: SqlExpr (Value UTCTime)
 now_ = unsafeSqlValue "NOW()"
+
+upsert :: (MonadIO m,
+      PersistEntity record,
+      OnlyOneUniqueKey record,
+      PersistRecordBackend record SqlBackend,
+      IsPersistBackend (PersistEntityBackend record))
+    => record
+    -- ^ new record to insert
+    -> [SqlExpr (Update record)]
+    -- ^ updates to perform if the record already exists
+    -> R.ReaderT SqlBackend m (Entity record)
+    -- ^ the record in the database after the operation
+upsert record updates = do
+    uniqueKey <- onlyUnique record
+    upsertBy uniqueKey record updates
+
+upsertBy :: (MonadIO m,
+    PersistEntity record,
+    IsPersistBackend (PersistEntityBackend record))
+  => Unique record
+  -- ^ uniqueness constraint to find by
+  -> record
+  -- ^ new record to insert
+  -> [SqlExpr (Update record)]
+  -- ^ updates to perform if the record already exists
+  -> R.ReaderT SqlBackend m (Entity record)
+  -- ^ the record in the database after the operation
+upsertBy uniqueKey record updates = do
+  sqlB <- R.ask
+  maybe
+    (throw (UnexpectedCaseErr OperationNotSupported)) -- Postgres backend should have connUpsertSql, if this error is thrown, check changes on persistent 
+    (handler sqlB)
+    (connUpsertSql sqlB)
+  where
+    addVals l = map toPersistValue (toPersistFields record) ++ l ++ persistUniqueToValues uniqueKey
+    entDef = entityDef (Just record)
+    uDef = head $ filter ((==) (persistUniqueToFieldNames uniqueKey) . uniqueFields) $ entityUniques entDef
+    updatesText conn = first builderToText $ renderUpdates conn updates
+    handler conn f = fmap head $ uncurry rawSql $
+      (***) (f entDef (uDef :| [])) addVals $ updatesText conn
+    renderUpdates :: SqlBackend
+        -> [SqlExpr (Update val)]
+        -> (TLB.Builder, [PersistValue])
+    renderUpdates conn = uncommas' . concatMap renderUpdate
+        where
+          mk (ERaw _ f)        = [f info]
+          mk (ECompositeKey _) = throw (CompositeKeyErr MakeSetError) -- FIXME
+          renderUpdate (ESet f) = mk (f undefined) -- second parameter of f is always unused
+          info = (projectBackend conn, initialIdentState)
\ No newline at end of file