diff --git a/System/Lock/FLock.hsc b/System/Lock/FLock.hsc
--- a/System/Lock/FLock.hsc
+++ b/System/Lock/FLock.hsc
@@ -48,6 +48,6 @@
                     NoBlock -> op .|. c_LOCK_NB
 
 unlock :: MonadIO m => Lock -> m ()
-unlock (Lock fd) = liftIO $ do flock fd c_LOCK_UN
+unlock (Lock fd) = liftIO $ do _ <- flock fd c_LOCK_UN
                                closeFd (Fd fd)
 
diff --git a/flock.cabal b/flock.cabal
--- a/flock.cabal
+++ b/flock.cabal
@@ -1,5 +1,5 @@
 Name:               flock
-Version:            0.1
+Version:            0.2
 License:            OtherLicense
 License-File:       COPYING
 Copyright:          Ian Lynagh, 2007
@@ -10,11 +10,13 @@
 Description:
     Simple wrapper around flock(2).
 Category:           System
-Tested-With:        GHC==6.6
-Build-Depends:      base, unix, mtl
+Build-Type:         Simple
+Tested-With:        GHC==6.10.3, GHC==6.12.3
+Cabal-Version:      >= 1.6
+Build-Depends:      base > 3 && < 5, unix >= 2.3 && < 2.5, mtl == 1.1.*
 Extensions:         ForeignFunctionInterface
 Extra-source-files: "BSD3", "GPL-2"
 Exposed-modules:
     System.Lock.FLock
-GHC-Options: -Wall -Werror
+GHC-Options: -Wall