diff --git a/dawg-ord.cabal b/dawg-ord.cabal
--- a/dawg-ord.cabal
+++ b/dawg-ord.cabal
@@ -1,5 +1,5 @@
 name:               dawg-ord
-version:            0.5.0.1
+version:            0.5.0.2
 synopsis:           Directed acyclic word graphs
 description:
     The library implements /directed acyclic word graphs/ (DAWGs) internally
@@ -32,7 +32,7 @@
       , containers      >= 0.5      && < 0.6
       , vector          >= 0.10     && < 0.12
       , mtl             >= 2.1      && < 2.3
-      , transformers    >= 0.3      && < 0.5
+      , transformers    >= 0.3      && < 0.6
 
     exposed-modules:
         Data.DAWG.Ord
diff --git a/src/Data/DAWG/Gen/HashMap.hs b/src/Data/DAWG/Gen/HashMap.hs
--- a/src/Data/DAWG/Gen/HashMap.hs
+++ b/src/Data/DAWG/Gen/HashMap.hs
@@ -86,7 +86,7 @@
 
 -- | Convert a regular map into a hash value (and into a 'Single'
 -- form if possible).
-trySingle :: Ord a => M.Map a b -> Value a b
+trySingle :: M.Map a b -> Value a b
 trySingle m = if M.size m == 1
     then uncurry Single (M.findMin m)
     else Multi m
diff --git a/src/Data/DAWG/Ord/Dynamic.hs b/src/Data/DAWG/Ord/Dynamic.hs
--- a/src/Data/DAWG/Ord/Dynamic.hs
+++ b/src/Data/DAWG/Ord/Dynamic.hs
@@ -167,7 +167,7 @@
 
 
 -- | Find value associated with the key.
-lookup :: (Ord a, Ord b) => [a] -> DAWG a b -> Maybe b
+lookup :: (Ord a) => [a] -> DAWG a b -> Maybe b
 lookup xs0 DAWG{..} = do
     xs <- mapM (`M.lookup` symMap) xs0
     y  <- D.lookup xs intDAWG