diff --git a/Data/Encoding/Preprocessor/Mapping.hs b/Data/Encoding/Preprocessor/Mapping.hs
index 9502517..c899b8f 100644
--- a/Data/Encoding/Preprocessor/Mapping.hs
+++ b/Data/Encoding/Preprocessor/Mapping.hs
@@ -104,7 +104,8 @@ preprocessMapping tp src trg mods name = do
                                                       Nothing -> Nothing
                                                       Just rc -> Just (rc,fromIntegral i::Word16)) trans)-}
   writeFile trg $ unlines $
-                ["{-# LANGUAGE MagicHash,DeriveDataTypeable #-}"
+                ["{- This file has been auto-generated. Do not edit it. -}"
+                ,"{-# LANGUAGE MagicHash,DeriveDataTypeable #-}"
                 ,"module "++mod++"("++name++"(..)) where"
                 ,""
                 ,"import Data.Encoding.Base"
diff --git a/Data/Encoding/Preprocessor/XMLMappingBuilder.hs b/Data/Encoding/Preprocessor/XMLMappingBuilder.hs
index 31d27df..03e3e9b 100644
--- a/Data/Encoding/Preprocessor/XMLMappingBuilder.hs
+++ b/Data/Encoding/Preprocessor/XMLMappingBuilder.hs
@@ -41,7 +41,8 @@ createModuleFromFile (sbase,sfile) (tbase,tfile) = do
                [(min,max-min+1) | min <- bmin | max <- bmax]
                | (st,end,bfirst,blast,bmin,bmax) <- ranges xml ]
   writeFile (tbase</>tfile) $ unlines $
-             ["{-# LANGUAGE MagicHash,DeriveDataTypeable #-}"]++
+             ["{- This file has been auto-generated. Do not edit it. -}"
+             ,"{-# LANGUAGE MagicHash,DeriveDataTypeable #-}"]++
                 (case description xml of
                    Nothing -> []
                    Just str -> ["{- | "++str++" -}"]) ++