diff --git a/servant-server/src/Servant/Server/Internal/ServantErr.hs b/servant-server/src/Servant/Server/Internal/ServantErr.hs
index 4bf3fe56..0b58b6be 100644
--- a/servant-server/src/Servant/Server/Internal/ServantErr.hs
+++ b/servant-server/src/Servant/Server/Internal/ServantErr.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RecordWildCards   #-}
+{-# LANGUAGE DeriveDataTypeable #-}
 module Servant.Server.Internal.ServantErr where
 
 import           Control.Exception (Exception)