diff --git a/Data/Generics/Uniplate/Internal/Data.hs b/Data/Generics/Uniplate/Internal/Data.hs
--- a/Data/Generics/Uniplate/Internal/Data.hs
+++ b/Data/Generics/Uniplate/Internal/Data.hs
@@ -77,7 +77,7 @@
 
 
 hitTestQuery :: DataBox -> TypeKey -> Maybe Cache
-hitTestQuery from@(DataBox kfrom _) kto = inlinePerformIO $ do
+hitTestQuery from@(DataBox kfrom vfrom) kto = inlinePerformIO $ do
     mp <- readIORef hitTestCache
     let res = IntMap.lookup kfrom mp >>= IntMap.lookup kto
     case res of
@@ -85,8 +85,11 @@
         Nothing -> do
             let res = toCache $ hitTestAdd from kto IntMap.empty
             res2 <- Control.Exception.catch (return $! res) (\(_ :: SomeException) -> return Nothing)
-            let mp2 = IntMap.adjust (IntMap.insert kto res2) kfrom mp
-            writeIORef hitTestCache mp2
+            -- -- uncomment these lines to see where type search fails
+            -- if isNothing res2 then print ("failure",show (typeOf vfrom),kfrom,kto) else return ()
+
+            atomicModifyIORef hitTestCache $ \mp -> flip (,) () $
+                IntMap.insertWith (const $ IntMap.insert kto res2) kfrom (IntMap.singleton kto res2) mp
             return res2
 
 
@@ -100,7 +103,7 @@
     where f x = IntMap.keysSet $ IntMap.filter (== x) res
 
 hitTestAdd :: DataBox -> TypeKey -> IntMap Res -> IntMap Res
-hitTestAdd (DataBox kfrom from) kto res = case sybChildren from of
+hitTestAdd from@(DataBox kfrom _) kto res = case sybChildren from of
     _ | kfrom `IntMap.member` res -> res
     Nothing -> IntMap.insert kfrom RBad res
 
@@ -133,14 +136,18 @@
 
 -- return all the possible children of a node
 -- if you can't do so, just return Nothing
-sybChildren :: Data a => a -> Maybe [DataBox]
-sybChildren x | isAlgType dtyp = Just $ concatMap f ctrs
-              | isNorepType dtyp = Nothing
-              | otherwise = Just []
+sybChildren :: DataBox -> Maybe [DataBox]
+sybChildren (DataBox k x)
+    | k == typeRational = Just [dataBox (0 :: Integer)]
+    | isAlgType dtyp = Just $ concatMap f ctrs
+    | isNorepType dtyp = Nothing
+    | otherwise = Just []
     where
         f ctr = gmapQ dataBox (asTypeOf (fromConstr ctr) x)
         ctrs = dataTypeConstrs dtyp
         dtyp = dataTypeOf x
+
+typeRational = typeKey (undefined :: Rational)
 
 #endif
 
diff --git a/Data/Generics/Uniplate/Internal/OperationsInc.hs b/Data/Generics/Uniplate/Internal/OperationsInc.hs
--- a/Data/Generics/Uniplate/Internal/OperationsInc.hs
+++ b/Data/Generics/Uniplate/Internal/OperationsInc.hs
@@ -1,5 +1,4 @@
 import Control.Monad(liftM)
-import Data.List(inits,tails)
 import Data.Traversable
 import Prelude hiding (mapM)
 import Data.Generics.Str
diff --git a/uniplate.cabal b/uniplate.cabal
--- a/uniplate.cabal
+++ b/uniplate.cabal
@@ -1,8 +1,8 @@
 Cabal-Version:      >= 1.2
 Build-Type:         Simple
 Name:               uniplate
-Version:            1.3
-Copyright:          2006-9, Neil Mitchell
+Version:            1.4
+Copyright:          2006-10, Neil Mitchell
 Maintainer:         ndmitchell@gmail.com
 Homepage:           http://community.haskell.org/~ndm/uniplate/
 License:            BSD3