diff --git a/src/Database/PostgreSQL/Aff.js b/src/Database/PostgreSQL/Aff.js
index 431ea0a..52db2ee 100644
--- a/src/Database/PostgreSQL/Aff.js
+++ b/src/Database/PostgreSQL/Aff.js
@@ -79,6 +79,7 @@ exports.ffiSQLState = function (error) {
 
 exports.ffiErrorDetail = function (error) {
     return {
+        error: error,
         severity: error.severity || '',
         code: error.code || '',
         message: error.message || '',
diff --git a/src/Database/PostgreSQL/Aff.purs b/src/Database/PostgreSQL/Aff.purs
index 9576ea7..cbda9e7 100644
--- a/src/Database/PostgreSQL/Aff.purs
+++ b/src/Database/PostgreSQL/Aff.purs
@@ -32,6 +32,7 @@ import Data.Nullable (Nullable, toMaybe, toNullable)
 import Data.Profunctor (lcmap)
 import Data.String (Pattern(..))
 import Data.String as String
+import Data.Symbol (SProxy(..))
 import Data.Traversable (traverse)
 import Database.PostgreSQL.Pool (Pool)
 import Database.PostgreSQL.Row (class FromSQLRow, class ToSQLRow, Row0(..), Row1(..), fromSQLRow, toSQLRow)
@@ -42,6 +43,7 @@ import Effect.Aff.Compat (EffectFnAff, fromEffectFnAff)
 import Effect.Class (liftEffect)
 import Effect.Exception (Error)
 import Foreign (Foreign)
+import Record (delete) as Record
 import Unsafe.Coerce (unsafeCoerce)
 
 -- | PostgreSQL connection.
@@ -113,7 +115,7 @@ withTransaction pool action =
     Right client ->
       withClientTransaction client do
         (action $ fromClient client)
-    Left err → pure $ Left err
+    Left err -> pure $ Left err
 
 -- | TODO: Outdated docs
 -- | Run an action within a transaction. The transaction is committed if the
@@ -161,7 +163,7 @@ fromClient client = Connection (Right client)
 
 -- | APIs of the `Pool.query` and `Client.query` are the same.
 -- | We can dse this polyformphis to simplify ffi.
-foreign import data UntaggedConnection ∷ Type
+foreign import data UntaggedConnection :: Type
 
 -- | Execute a PostgreSQL query and discard its results.
 execute ::
@@ -222,7 +224,7 @@ unsafeQuery ::
   Aff (Either PGError QueryResult)
 unsafeQuery conn s = fromEffectFnAff <<< ffiUnsafeQuery p (toUntaggedHandler conn) s
   where
-  toUntaggedHandler ∷ Connection → UntaggedConnection
+  toUntaggedHandler :: Connection -> UntaggedConnection
   toUntaggedHandler (Connection c) = case c of
     (Left pool) -> unsafeCoerce pool
     (Right client) -> unsafeCoerce client
@@ -242,7 +244,7 @@ foreign import ffiUnsafeQuery ::
   EffectFnAff (Either PGError QueryResult)
 
 data PGError
-  = ClientError String
+  = ClientError Error String
   | ConversionError String
   | InternalError PGErrorDetail
   | OperationalError PGErrorDetail
@@ -253,7 +255,26 @@ data PGError
   | QueryCanceledError PGErrorDetail
   | TransactionRollbackError PGErrorDetail
 
-derive instance eqPGError :: Eq PGError
+-- | Those instances are required for testing.
+instance eqPGError :: Eq PGError where
+  eq = case _, _ of
+    (ClientError _ s1), (ClientError _ s2) -> s1 == s2
+    (ConversionError s1), (ConversionError s2) -> s1 == s2
+    (InternalError err1), (InternalError err2) -> eqErr err1 err2
+    (OperationalError err1), (OperationalError err2) -> eqErr err1 err2
+    (ProgrammingError err1), (ProgrammingError err2) -> eqErr err1 err2
+    (IntegrityError err1), (IntegrityError err2) -> eqErr err1 err2
+    (DataError err1), (DataError err2) -> eqErr err1 err2
+    (NotSupportedError err1), (NotSupportedError err2) -> eqErr err1 err2
+    (QueryCanceledError err1), (QueryCanceledError err2) -> eqErr err1 err2
+    (TransactionRollbackError err1), (TransactionRollbackError err2) -> eqErr err1 err2
+    _, _ -> false
+    where
+    eqErr err1 err2 =
+      let
+        _error = SProxy :: SProxy "error"
+      in
+        eq (Record.delete _error err1) (Record.delete _error err2)
 
 derive instance genericPGError :: Generic PGError _
 
@@ -265,6 +286,7 @@ type PGErrorDetail
     , code :: String
     , message :: String
     , detail :: String
+    , error :: Error
     , hint :: String
     , position :: String
     , internalPosition :: String
@@ -345,7 +367,7 @@ convertError err = case toMaybe $ ffiSQLState err of
                                       if prefix "X" s then
                                         InternalError
                                       else
-                                        const $ ClientError s
+                                        const $ ClientError err s
 
   prefix :: String -> String -> Boolean
   prefix p = maybe false (_ == 0) <<< String.indexOf (Pattern p)
diff --git a/test/Main.purs b/test/Main.purs
index 9d4fa4e..f807ad3 100644
--- a/test/Main.purs
+++ b/test/Main.purs
@@ -3,7 +3,6 @@ module Test.Main
   ) where
 
 import Prelude
-
 import Control.Monad.Error.Class (throwError, try)
 import Control.Monad.Except.Trans (runExceptT)
 import Control.Monad.Trans.Class (lift)
@@ -59,6 +58,7 @@ withRollback ∷
 withRollback client action = begin *> action *> rollback
   where
   conn = fromClient client
+
   begin = execute conn (Query "BEGIN TRANSACTION") Row0
 
   rollback = execute conn (Query "ROLLBACK TRANSACTION") Row0
@@ -69,6 +69,7 @@ test ∷
   AppM Unit →
   TestSuite
 test (Connection (Left pool)) name action = Test.Unit.test name $ checkPGErrors $ action
+
 test (Connection (Right client)) name action = Test.Unit.test name $ checkPGErrors $ withRollback client action
 
 transactionTest ∷
@@ -471,7 +472,7 @@ main = do
                             testPool <- liftEffect $ Pool.new (cannotConnectConfig config)
                             runExceptT (withClient testPool doNothing)
                               >>= case _ of
-                                  Left (ClientError cause) -> equal cause "ECONNREFUSED"
+                                  Left (ClientError _ cause) -> equal cause "ECONNREFUSED"
                                   _ -> Test.Unit.failure "foo"
                           Test.Unit.test "no such database" do
                             testPool <- liftEffect $ Pool.new (noSuchDatabaseConfig config)