diff --git a/Control/Concurrent/Chan/Strict.hs b/Control/Concurrent/Chan/Strict.hs
--- a/Control/Concurrent/Chan/Strict.hs
+++ b/Control/Concurrent/Chan/Strict.hs
@@ -41,6 +41,7 @@
 
 import System.IO.Unsafe         ( unsafeInterleaveIO )
 import Control.Concurrent.MVar.Strict
+import Control.Parallel.Strategies
 
 -- A channel is represented by two @MVar@s keeping track of the two ends
 -- of the channel contents,i.e.,  the read- and write ends. Empty @MVar@s
@@ -55,11 +56,16 @@
 
 data ChItem a = ChItem !a (Stream a)
 
+instance NFData (MVar a)
+
+instance NFData a => NFData (ChItem a) where
+    rnf (ChItem a s) = rnf a `seq` rnf s
+
 -- @newChan@ sets up the read and write end of a channel by initialising
 -- these two @MVar@s with an empty @MVar@.
 
 -- |Build and returns a new instance of 'Chan'.
-newChan :: IO (Chan a)
+newChan :: NFData a => IO (Chan a)
 newChan = do
    hole  <- newEmptyMVar
    readm <- newMVar hole
@@ -72,7 +78,7 @@
 -- new hole.
 
 -- |Write a value to a 'Chan'.
-writeChan :: Chan a -> a -> IO ()
+writeChan :: NFData a => Chan a -> a -> IO ()
 writeChan (Chan _read write) val = do
   new_hole <- newEmptyMVar
   modifyMVar_ write $ \old_hole -> do
@@ -80,7 +86,7 @@
     return new_hole
 
 -- |Read the next value from the 'Chan'.
-readChan :: Chan a -> IO a
+readChan :: NFData a => Chan a -> IO a
 readChan (Chan readm _write) = do
   modifyMVar readm $ \read_end -> do
     (ChItem val new_read_end) <- readMVar read_end
@@ -92,14 +98,14 @@
 -- either channel from then on will be available from both.  Hence this creates
 -- a kind of broadcast channel, where data written by anyone is seen by
 -- everyone else.
-dupChan :: Chan a -> IO (Chan a)
+dupChan :: NFData a => Chan a -> IO (Chan a)
 dupChan (Chan _read write) = do
    hole     <- readMVar write
    new_read <- newMVar hole
    return (Chan new_read write)
 
 -- |Put a data item back onto a channel, where it will be the next item read.
-unGetChan :: Chan a -> a -> IO ()
+unGetChan :: NFData a => Chan a -> a -> IO ()
 unGetChan (Chan readm _write) val = do
    new_read_end <- newEmptyMVar
    modifyMVar_ readm $ \read_end -> do
@@ -107,7 +113,7 @@
      return new_read_end
 
 -- |Returns 'True' if the supplied 'Chan' is empty.
-isEmptyChan :: Chan a -> IO Bool
+isEmptyChan ::NFData a =>  Chan a -> IO Bool
 isEmptyChan (Chan readm write) = do
    withMVar readm $ \r -> do
      w <- readMVar write
@@ -118,12 +124,12 @@
 
 -- |Return a lazy list representing the contents of the supplied
 -- 'Chan', much like 'System.IO.hGetContents'.
-getChanContents :: Chan a -> IO [a]
+getChanContents ::NFData a =>  Chan a -> IO [a]
 getChanContents ch = unsafeInterleaveIO $ do
     x  <- readChan ch
     xs <- getChanContents ch
     return (x:xs)
 
 -- |Write an entire list of items to a 'Chan'.
-writeList2Chan :: Chan a -> [a] -> IO ()
+writeList2Chan ::NFData a =>  Chan a -> [a] -> IO ()
 writeList2Chan = mapM_ . writeChan
diff --git a/Control/Concurrent/MVar/Strict.hs b/Control/Concurrent/MVar/Strict.hs
--- a/Control/Concurrent/MVar/Strict.hs
+++ b/Control/Concurrent/MVar/Strict.hs
@@ -11,7 +11,7 @@
 --
 -- Synchronising, strict variables
 --
--- Values placed in an MVar are evaluated to weak-head normal form
+-- Values placed in an MVar are evaluated to head normal form
 -- before being placed in the MVar, preventing a common source of
 -- space-leaks involving synchronising variables.
 --
@@ -44,6 +44,7 @@
 
 import Prelude
 import Control.Exception as Exception
+import Control.Parallel.Strategies
 
 -- |Put a value into an 'MVar'.  If the 'MVar' is currently full,
 -- 'putMVar' will wait until it becomes empty.
@@ -59,9 +60,9 @@
 --     woken up in FIFO order.  This is useful for providing
 --     fairness properties of abstractions built using 'MVar's.
 --
-putMVar  :: MVar a -> a -> IO ()
+putMVar  :: NFData a => MVar a -> a -> IO ()
 #ifndef __HADDOCK__
-putMVar (MVar mvar#) !x = IO $ \ s# -> -- strict!
+putMVar (MVar mvar#) !x = rnf x `seq` IO $ \ s# -> -- strict!
     case putMVar# mvar# x s# of
         s2# -> (# s2#, () #)
 #endif
@@ -70,7 +71,7 @@
 -- attempts to put the value @a@ into the 'MVar', returning 'True' if
 -- it was successful, or 'False' otherwise.
 --
-tryPutMVar  :: MVar a -> a -> IO Bool
+tryPutMVar  :: NFData a => MVar a -> a -> IO Bool
 #ifndef __HADDOCK__
 tryPutMVar (MVar mvar#) !x = IO $ \ s# -> -- strict!
     case tryPutMVar# mvar# x s# of
@@ -79,7 +80,7 @@
 #endif
 
 -- |Create an 'MVar' which contains the supplied value.
-newMVar :: a -> IO (MVar a)
+newMVar :: NFData a => a -> IO (MVar a)
 newMVar value =
     newEmptyMVar        >>= \ mvar ->
     putMVar mvar value  >>
@@ -89,7 +90,7 @@
   This is a combination of 'takeMVar' and 'putMVar'; ie. it takes the value
   from the 'MVar', puts it back, and also returns it.
 -}
-readMVar :: MVar a -> IO a
+readMVar :: NFData a => MVar a -> IO a
 readMVar m = block $ do
     a <- takeMVar m
     putMVar m a
@@ -101,7 +102,7 @@
   another process can put something in the 'MVar' after the take
   happens but before the put does.
 -}
-swapMVar :: MVar a -> a -> IO a
+swapMVar :: NFData a => MVar a -> a -> IO a
 swapMVar mvar new = block $ do
     old <- takeMVar mvar
     putMVar mvar new
@@ -116,7 +117,7 @@
 {-# INLINE withMVar #-}
 -- inlining has been reported to have dramatic effects; see
 -- http://www.haskell.org//pipermail/haskell/2006-May/017907.html
-withMVar :: MVar a -> (a -> IO b) -> IO b
+withMVar :: NFData a => MVar a -> (a -> IO b) -> IO b
 withMVar m io = block $ do
     a <- takeMVar m
     b <- Exception.catch (unblock (io a))
@@ -130,7 +131,7 @@
   exception is raised during the operation.
 -}
 {-# INLINE modifyMVar_ #-}
-modifyMVar_ :: MVar a -> (a -> IO a) -> IO ()
+modifyMVar_ :: NFData a => MVar a -> (a -> IO a) -> IO ()
 modifyMVar_ m io = block $ do
     a  <- takeMVar m
     a' <- Exception.catch (unblock (io a))
@@ -142,10 +143,11 @@
   returned (@b@) in addition to the modified value of the 'MVar'.
 -}
 {-# INLINE modifyMVar #-}
-modifyMVar :: MVar a -> (a -> IO (a,b)) -> IO b
+modifyMVar :: NFData a => MVar a -> (a -> IO (a,b)) -> IO b
 modifyMVar m io = block $ do
     a      <- takeMVar m
     (a',b) <- Exception.catch (unblock (io a))
                 (\e -> do putMVar m a; throw e)
     putMVar m a'
     return b
+
diff --git a/strict-concurrency.cabal b/strict-concurrency.cabal
--- a/strict-concurrency.cabal
+++ b/strict-concurrency.cabal
@@ -1,22 +1,23 @@
 Name:           strict-concurrency
-Version:        0.1
+Version:        0.2
 Synopsis:       Strict concurrency abstractions
 Category:       Control
 Description:
-        This package provides strict versions of some standard Haskell
-        concurrency abstractions (MVars,Chans), which provide control
-        over where evaluation takes place not offered by the default
-        lazy types. This may be useful for deciding when and where 
-        evaluation occurs, leading to improved time or space use,
+        This package provides head normal form strict versions of some
+        standard Haskell concurrency abstractions (MVars,Chans), which
+        provide control over where evaluation takes place not offered by
+        the default lazy types. This may be useful for deciding when and
+        where evaluation occurs, leading to improved time or space use,
         depending on the circumstances.
 License:        BSD3
 License-File:   LICENSE
 Author:         Don Stewart <dons@galois.com>
 Maintainer:     Don Stewart <dons@galois.com>
-Copyright:      (c) 2007 Don Stewart
+Copyright:      (c) 2007-8 Don Stewart
 Homepage:       http://code.haskell.org/~dons/code/strict-concurrency
-build-depends:  base
-ghc-options:    -Wall -Werror -fglasgow-exts
-extensions:     CPP
+build-depends:  base, parallel
+ghc-options:    -Wall -fglasgow-exts
+extensions:     CPP, BangPatterns
+build-type:     Simple
 exposed-modules: Control.Concurrent.MVar.Strict
                  Control.Concurrent.Chan.Strict
diff --git a/tests/chan-test.hs b/tests/chan-test.hs
--- a/tests/chan-test.hs
+++ b/tests/chan-test.hs
@@ -21,8 +21,13 @@
         forkIO (writeList2Chan c f)
         return l
 
--- lazily returns values to the main thread to compute, should run twice
--- as fast if we compute in the worker thread
-fibonacci = 0 : 1 : zipWith (+) fibonacci (tail fibonacci)
+--
+-- very computationally expensive jobs:
 
-fibonacci2 = 1 : 1 : zipWith (+) fibonacci2 (tail fibonacci2)
+fibonacci = map fib [0..]
+
+fibonacci2 = map fib [1..] -- to defeat CSE
+
+fib 0 = 0
+fib 1 = 1
+fib n = fib (n-1) + fib (n-2)
diff --git a/tests/run-tests b/tests/run-tests
--- a/tests/run-tests
+++ b/tests/run-tests
@@ -1,7 +1,7 @@
 #!/bin/sh
 
+N=35
 M=5000000
-N=2000
 O=50000000
 
 ghc          -cpp -O -no-recomp -threaded --make mvar-test.hs -o lazy-mvar
@@ -13,6 +13,17 @@
 ghc          -cpp -O -no-recomp -threaded --make thread-ring.hs -o lazy-thread-ring
 ghc -DSTRICT -cpp -O -no-recomp -threaded --make thread-ring.hs -o strict-thread-ring
 
+echo "******* Testing Chans ************"
+ 
+echo "** Should be slow:"
+/usr/bin/time ./lazy-chan   $N +RTS -tstderr -RTS > /dev/null
+
+echo "** Should be fast:"
+/usr/bin/time ./strict-chan $N +RTS -tstderr -RTS > /dev/null
+
+echo "** Should be twice as fast (on 2 cores)"
+/usr/bin/time ./strict-chan $N +RTS -N2 -tstderr -RTS > /dev/null
+
 echo "******* Testing MVars ************"
  
 echo "** Should have a space leak:"
@@ -23,17 +34,6 @@
 
 echo "** Should pass (2 cores)"
 /usr/bin/time ./strict-mvar $M +RTS -N2 -tstderr -RTS > /dev/null
-
-echo "******* Testing Chans ************"
- 
-echo "** Should be slow:"
-/usr/bin/time ./lazy-chan   $N +RTS -tstderr -RTS > /dev/null
-
-echo "** Should be fast:"
-/usr/bin/time ./strict-chan $N +RTS -tstderr -RTS > /dev/null
-
-echo "** Should be fast (2 cores)"
-/usr/bin/time ./strict-chan $N +RTS -N2 -tstderr -RTS > /dev/null
 
 echo "******* Testing thread-ring benchmark ************"