diff --git a/Cabal.hs b/Cabal.hs
index eea919d..d47bc3f 100644
--- a/Cabal.hs
+++ b/Cabal.hs
@@ -14,6 +14,7 @@ import Distribution.Verbosity (silent)
 import ErrMsg
 import GHC
 import GHCApi
+import qualified Gap
 import Language.Haskell.Extension
 import System.Directory
 import System.FilePath
@@ -34,8 +35,8 @@ initializeGHC opt fileName ghcOptions logging = withCabal <|> withoutCabal
         (owdir,cdir,cfile) <- liftIO getDirs
         binfo <- liftIO $ parseCabalFile cfile
         let (idirs',exts',mlang) = extractBuildInfo binfo
-            exts = map addX exts'
-            lang = maybe "-XHaskell98" addX mlang
+            exts = map (addX . Gap.extensionToString)  exts'
+            lang = maybe "-XHaskell98" (addX . show) mlang
             gopts = ghcOptions ++ exts ++ [lang]
         changeToCabalDirectory cdir
         let idirs = case idirs' of
@@ -44,7 +45,7 @@ initializeGHC opt fileName ghcOptions logging = withCabal <|> withoutCabal
             file = ajustFileName fileName owdir cdir
         logReader <- initSession opt gopts idirs logging
         return (file,logReader)
-    addX x = "-X" ++ show x
+    addX = ("-X" ++)
 
 ----------------------------------------------------------------
 
diff --git a/Gap.hs b/Gap.hs
index 828b1e6..046dcd9 100644
--- a/Gap.hs
+++ b/Gap.hs
@@ -9,6 +9,7 @@ module Gap (
   , fOptions
   , toStringBuffer
   , liftIO
+  , extensionToString
 #if __GLASGOW_HASKELL__ >= 702
 #else
   , module Pretty
@@ -21,6 +22,7 @@ import Control.Monad
 import DynFlags
 import FastString
 import GHC
+import Language.Haskell.Extension
 import Outputable
 import StringBuffer
 
@@ -119,3 +121,15 @@ setCtx ms = do
       where
         lookupMod = lookupModule (ms_mod_name mos) Nothing >> return True
         returnFalse = return False
+
+----------------------------------------------------------------
+-- This is Cabal, not GHC API
+
+extensionToString :: Extension -> String
+#if __GLASGOW_HASKELL__ == 704
+extensionToString (EnableExtension ext)  = show ext
+extensionToString (DisableExtension ext) = show ext -- FIXME
+extensionToString (UnknownExtension ext) = ext
+#else
+extensionToString = show
+#endif