diff --git a/src/compiler/GF/Compile/ReadFiles.hs b/src/compiler/GF/Compile/ReadFiles.hs
index 3182e192c..9396b3a2f 100644
--- a/src/compiler/GF/Compile/ReadFiles.hs
+++ b/src/compiler/GF/Compile/ReadFiles.hs
@@ -20,7 +20,7 @@
 
 module GF.Compile.ReadFiles
            ( getAllFiles,ModName,ModEnv,importsOfModule,
-             findFile,gfImports,gfoImports,
+             findFile,gfImports,gfoImports,VersionTagged(..),
              parseSource,getOptionsFromFile,getPragmas) where
 
 import Prelude hiding (catch)
@@ -32,7 +32,7 @@ import GF.Data.Operations
 import GF.Grammar.Lexer
 import GF.Grammar.Parser
 import GF.Grammar.Grammar
-import GF.Grammar.Binary(decodeModuleHeader)
+import GF.Grammar.Binary(VersionTagged(..),decodeModuleHeader)
 
 import System.IO(mkTextEncoding)
 import GF.Text.Coding(decodeUnicodeIO)
@@ -107,10 +107,10 @@ getAllFiles opts ps env file = do
           case st of
             CSEnv  -> return (st, (name, maybe [] snd mb_envmod))
             CSRead -> do let gfo = if isGFO file then file else gf2gfo opts file
-                         mb_imps <- gfoImports gfo
-                         case mb_imps of
-                           Just imps -> return (st,imps)
-                           Nothing
+                         t_imps <- gfoImports gfo
+                         case t_imps of
+                           Tagged imps -> return (st,imps)
+                           WrongVersion
                              | isGFO file -> raise (file ++ " is compiled with different GF version and I can't find the source file")
                              | otherwise  -> do imps <- gfImports opts file
                                                 return (CSComp,imps)
@@ -143,7 +143,7 @@ findFile gfoDir ps name =
 
 gfImports opts file = importsOfModule `fmap` parseModHeader opts file
 
-gfoImports gfo = fmap importsOfModule `fmap` liftIO (decodeModuleHeader gfo)
+gfoImports gfo = fmap importsOfModule `fmap` decodeModuleHeader gfo
 
 --------------------------------------------------------------------------------
 
diff --git a/src/compiler/GF/CompileInParallel.hs b/src/compiler/GF/CompileInParallel.hs
index 4f5c0f76b..07c29febd 100644
--- a/src/compiler/GF/CompileInParallel.hs
+++ b/src/compiler/GF/CompileInParallel.hs
@@ -9,7 +9,7 @@ import qualified GF.System.Directory as D
 import GF.System.Catch(catch,try)
 import Data.List(nub,isPrefixOf,intercalate,partition)
 import qualified Data.Map as M
-import GF.Compile.ReadFiles(getOptionsFromFile,findFile,gfImports,gfoImports)
+import GF.Compile.ReadFiles(getOptionsFromFile,findFile,gfImports,gfoImports,VersionTagged(..))
 import GF.CompileOne(reuseGFO,useTheSource)
 import GF.Infra.Option
 import GF.Infra.UseIO
@@ -177,8 +177,10 @@ getPathFromFile lib_dir cmdline_opts file =
 getImports opts file =
     if isGFO file then gfoImports' file else gfImports opts file
   where
-    gfoImports' file = maybe bad return =<< gfoImports file
-      where bad = raise $ file++": bad .gfo file"
+    gfoImports' file = check =<< gfoImports file
+      where
+        check (Tagged imps) = return imps
+        check WrongVersion = raise $ file++": .gfo file version mismatch"
 
 relativeTo lib_dir cwd path =
     if length librel<length cwdrel then librel else cwdrel
diff --git a/src/compiler/GF/Grammar/Binary.hs b/src/compiler/GF/Grammar/Binary.hs
index 5aed63363..725ae9284 100644
--- a/src/compiler/GF/Grammar/Binary.hs
+++ b/src/compiler/GF/Grammar/Binary.hs
@@ -7,15 +7,13 @@
 --
 -----------------------------------------------------------------------------
 
-module GF.Grammar.Binary(decodeModule,decodeModuleHeader,encodeModule) where
+module GF.Grammar.Binary(VersionTagged(..),decodeModuleHeader,decodeModule,encodeModule) where
 
 import Prelude hiding (catch)
 import Control.Exception(catch,ErrorCall(..),throwIO)
 
---import Data.Char
 import PGF.Internal(Binary(..),Word8,putWord8,getWord8,encodeFile,decodeFile)
---import Control.Monad
-import qualified Data.Map as Map
+import qualified Data.Map as Map(empty)
 import qualified Data.ByteString.Char8 as BS
 
 import GF.Data.Operations
@@ -28,7 +26,7 @@ import PGF() -- Binary instances
 import PGF.Internal(Literal(..))
 
 -- Please change this every time when the GFO format is changed
-gfoVersion = "GF03"
+gfoVersion = "GF04"
 
 instance Binary Ident where
   put id = put (ident2utf8 id)
@@ -315,6 +313,10 @@ instance Binary a => Binary (VersionTagged a) where
              then fmap Tagged get
              else return WrongVersion
 
+instance Functor VersionTagged where
+  fmap f (Tagged a) = Tagged (f a)
+  fmap f WrongVersion = WrongVersion
+
 gfoBinVersion = (b1,b2,b3,b4)
   where [b1,b2,b3,b4] = map (toEnum.fromEnum) gfoVersion :: [Word8]
 
@@ -324,23 +326,14 @@ decodeModule fpath = liftIO $ check =<< decodeFile' fpath
   where
     check (Tagged m) = return m
     check _ = fail ".gfo file version mismatch"
-{-
-decodeModuleHeader fpath = decodeFile_ fpath getVersionedMod
+
+-- | Read just the module header, the returned 'Module' will have an empty body
+decodeModuleHeader :: MonadIO io => FilePath -> io (VersionTagged Module)
+decodeModuleHeader = liftIO . fmap (fmap conv) . decodeFile'
   where
-    getVersionedMod = do
-      ver <- getGFOVersion
-      if ver == gfoVersion
-        then do (m,mtype,mstatus,mflags,mextend,mwith,mopens,med,msrc) <- get
-                return (Just (m,ModInfo mtype mstatus mflags mextend mwith mopens med msrc Nothing Map.empty))
-        else return Nothing
---}
---{-
-decodeModuleHeader fpath = fmap check $ decodeFile' fpath
-  where
-    check (Tagged (m,mtype,mstatus,mflags,mextend,mwith,mopens,med,msrc)) =
-        (Just (m,ModInfo mtype mstatus mflags mextend mwith mopens med msrc Nothing Map.empty))
-    check _ = Nothing
---}
+    conv (m,mtype,mstatus,mflags,mextend,mwith,mopens,med,msrc) =
+        (m,ModInfo mtype mstatus mflags mextend mwith mopens med msrc Nothing Map.empty)
+
 encodeModule :: MonadIO io => FilePath -> SourceModule -> io ()
 encodeModule fpath mo = liftIO $ encodeFile fpath (Tagged mo)
 
diff --git a/src/runtime/haskell/PGF/Binary.hs b/src/runtime/haskell/PGF/Binary.hs
index a7f6bf881..e0e50f4be 100644
--- a/src/runtime/haskell/PGF/Binary.hs
+++ b/src/runtime/haskell/PGF/Binary.hs
@@ -15,7 +15,7 @@ import qualified Data.IntMap as IntMap
 import Control.Monad
 
 pgfMajorVersion, pgfMinorVersion :: Word16
-version@(pgfMajorVersion, pgfMinorVersion) = (2,0)
+version@(pgfMajorVersion, pgfMinorVersion) = (2,1)
 
 instance Binary PGF where
   put pgf = do putWord16be pgfMajorVersion
@@ -23,11 +23,14 @@ instance Binary PGF where
                put (gflags pgf)
                put (absname pgf, abstract pgf)
                put (concretes pgf)
-  get = do v1 <- getWord16be
-           v2 <- getWord16be
-           case (v1,v2) of
-             v | v==version -> getPGF'
-               | v==Old.version -> Old.getPGF'
+  get = do major<- getWord16be
+           minor <- getWord16be
+           let v = (major,minor)
+           if major==pgfMajorVersion && minor<=pgfMinorVersion
+             then getPGF'
+             else if v==Old.version 
+                  then Old.getPGF'
+                  else fail $ "Unsupported PGF version "++show (major,minor)
 
 getPGF'=do gflags <- get
            (absname,abstract) <- get