diff --git a/src/PDF/Box.hs b/src/PDF/Box.hs
index 23817d5..f43a3f8 100644
--- a/src/PDF/Box.hs
+++ b/src/PDF/Box.hs
@@ -20,6 +20,8 @@ import Control.Monad.State (MonadState(..))
 --import Control.Monad.Reader (MonadReader(..))
 import Data.Map (Map)
 import qualified Data.Map as Map (insert, lookup, member)
+import Data.OrderedMap (OrderedMap)
+import qualified Data.OrderedMap as OrderedMap (lookup, set)
 import Prelude hiding (fail)
 
 {-
@@ -66,6 +68,10 @@ instance (Ord k, MonadFail m) => Box m k (Map k a) a where
         return $ Map.insert k a aMap
     | otherwise = fail "Unknown key"
 
+instance (Ord k, MonadFail m) => Box m k (OrderedMap k a) a where
+  r k = maybe (fail "Unknown key") return . OrderedMap.lookup k
+  w k a orderedMap = r k orderedMap >> return (OrderedMap.set k a orderedMap)
+
 instance (Monad m, Box Maybe i a b) => Box m (Maybe_ i) a (Maybe b) where
   r (Maybe_ i) = return . r i
   w (Maybe_ i) (Just b) a =