This code demonstrates the problem: import Control.Concurrent import Control.Concurrent.Chan import Control.Monad test = do c <- newChan forkIO $ forever $ do i <- readChan c print i writeChan c 1 threadDelay 1000000 isEmptyChan c >>= print Test session: ben@sarun[1]: .../hca/current > ghci Bug5.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( Bug5.hs, interpreted ) Ok, modules loaded: Main. *Main> test 1 The program hangs here. This is a deadlock caused by the calls to isEmptyChan and readChan both waiting on the same MVar, as a quick look at the sources reveals. I don't have an immediate fix but is shouldn't be too hard to find one. I can try to, if it is consensus that this is a bug. Incidentally, if I replace Chan with TChan (and wrap all xxxTChan calls in an atomically), then this code terminates just fine. Cheers Ben