diff --git a/Crypto/Random.hs b/Crypto/Random.hs
--- a/Crypto/Random.hs
+++ b/Crypto/Random.hs
@@ -9,6 +9,7 @@
 -- random generator.
 --
 {-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE DeriveDataTypeable #-}
 module Crypto.Random
     (
     -- * Entropy
@@ -28,6 +29,7 @@
 import Crypto.Random.Entropy
 import Crypto.Random.Generator
 import Data.ByteString (ByteString)
+import Data.Typeable (Typeable)
 import qualified Data.ByteString.Internal as B (unsafeCreate)
 
 -- | System entropy generator.
@@ -39,6 +41,7 @@
 -- use for testing and debugging purpose, but otherwise for real world use case
 -- should be fine.
 data SystemRNG = SystemRNG EntropyPool
+  deriving Typeable
 
 instance CPRG SystemRNG where
     cprgCreate entPool                   = SystemRNG entPool
diff --git a/Crypto/Random/Entropy.hs b/Crypto/Random/Entropy.hs
--- a/Crypto/Random/Entropy.hs
+++ b/Crypto/Random/Entropy.hs
@@ -7,6 +7,7 @@
 --
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE DeriveDataTypeable #-}
 module Crypto.Random.Entropy
     ( EntropyPool
     , createEntropyPool
@@ -21,6 +22,7 @@
 import System.IO.Unsafe (unsafePerformIO)
 import Data.Maybe (catMaybes)
 import Data.SecureMem
+import Data.Typeable (Typeable)
 import Data.ByteString (ByteString)
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Internal as B
@@ -80,6 +82,7 @@
 -- | Pool of Entropy. contains a self mutating pool of entropy,
 -- that is always guarantee to contains data.
 data EntropyPool = EntropyPool [EntropyBackend] (MVar Int) SecureMem
+  deriving Typeable
 
 -- size of entropy pool by default
 defaultPoolSize :: Int
diff --git a/Crypto/Random/Test.hs b/Crypto/Random/Test.hs
--- a/Crypto/Random/Test.hs
+++ b/Crypto/Random/Test.hs
@@ -7,6 +7,8 @@
 --
 -- Provide way to test usual simple statisticals test for randomness
 --
+{-# LANGUAGE GADTs #-}
+
 module Crypto.Random.Test
     ( RandomTestState
     , RandomTestResult(..)
@@ -50,6 +52,7 @@
                 let (b1,b2) = L.splitAt monteN bs
                 mapM_ (addVec 1 . fromIntegral) $ L.unpack b1
                 loop b2
+        addVec :: Word64 -> Int -> IO ()
         addVec a i = M.read buckets i >>= \d -> M.write buckets i $! d+a
 
 -- | Finalize random test state into some result
diff --git a/crypto-random.cabal b/crypto-random.cabal
--- a/crypto-random.cabal
+++ b/crypto-random.cabal
@@ -1,5 +1,5 @@
 Name:                crypto-random
-Version:             0.0.7
+Version:             0.0.8
 Description:         Simple cryptographic random related types
 License:             BSD3
 License-file:        LICENSE