diff --git a/Data/FileCache.hs b/Data/FileCache.hs
--- a/Data/FileCache.hs
+++ b/Data/FileCache.hs
@@ -7,6 +7,7 @@
 import Control.Exception
 import Control.Monad
 import Control.Monad.Error.Class
+import Control.Exception.Lens
 
 data Messages r a = Invalidate !FilePath
                   | Query !FilePath !(IO (S.Either r a)) !(MVar (S.Either r a))
@@ -39,17 +40,22 @@
             Invalidate fp ->
                 case HM.lookup fp mp of
                     Nothing -> nochange
-                    Just (_,desc) -> removeWatch desc >> change (HM.delete fp)
+                    Just (_,desc) -> catching_ id (removeWatch desc) (return ()) >> change (HM.delete fp)
             Query fp action respvar ->
                 case HM.lookup fp mp of
                     Just (x,_) -> putMVar respvar x >> nochange
                     Nothing -> do
-                        valr <- catch action $ \e -> do
-                            let r = strMsg $ "Exception: " ++ show (e :: SomeException)
-                            return (S.Left r)
-                        wm <- addWatch ino [CloseWrite,Delete,Move,Attrib,Create] fp (const $ invalidate fp (FileCache q))
-                        putMVar respvar valr
-                        change (HM.insert fp (valr,wm))
+                        let addw value = do
+                                wm <- addWatch ino [CloseWrite,Delete,Move,Attrib,Create] fp (const $ invalidate fp (FileCache q))
+                                change (HM.insert fp (value,wm))
+                            withWatch value = do
+                                putMVar respvar value
+                                catching_ id (addw value) nochange
+                            noWatch x = putMVar respvar x >> nochange
+                        catches (action >>= withWatch)
+                            [ handler _IOException (\io -> noWatch   (S.Left (strMsg $ show io)))
+                            , handler id           (\e  -> withWatch (S.Left (strMsg $ show e)))
+                            ]
             GetCopy mv -> putMVar mv mp >> nochange
     case nmp of
         Just x -> mapMaster x q ino
diff --git a/filecache.cabal b/filecache.cabal
--- a/filecache.cabal
+++ b/filecache.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                filecache
-version:             0.2.0
+version:             0.2.1
 synopsis:            A Linux-only cache system associating values to files. The values are discarded when the files are modified.
 -- description:         
 homepage:            http://lpuppet.banquise.net/
@@ -15,8 +15,15 @@
 build-type:          Simple
 cabal-version:       >=1.8
 
+test-suite simpletest
+    hs-source-dirs: tests
+    type:           exitcode-stdio-1.0
+    ghc-options:    -Wall -rtsopts -threaded -with-rtsopts-N
+    build-depends:  base, filecache, temporary, directory, unordered-containers
+    main-is:        simpletest.hs
+
 library
   exposed-modules:     Data.FileCache
   ghc-options:         -Wall
   -- other-modules:       
-  build-depends:       base ==4.6.*, unordered-containers, hashable, hinotify, strict-base-types >= 0.2, mtl
+  build-depends:       base ==4.6.*, unordered-containers, hashable, hinotify, strict-base-types >= 0.2, mtl, lens
diff --git a/tests/simpletest.hs b/tests/simpletest.hs
new file mode 100644
--- /dev/null
+++ b/tests/simpletest.hs
@@ -0,0 +1,35 @@
+module Main where
+
+import System.IO.Temp
+import Data.FileCache
+import Control.Monad
+import Control.Exception
+import System.Directory
+import Control.Concurrent
+import qualified Data.HashMap.Strict as HM
+
+computation :: String -> IO (Either String Int)
+computation f = do
+    c <- readFile f
+    if length c `mod` 2 == 0
+        then return (Right (length c))
+        else return (Left "odd length")
+
+main :: IO ()
+main = withSystemTempDirectory "filecacheXXX.tmp" $ \tempdir -> do
+    cache <- newFileCache :: IO (FileCache Int)
+    let indexes = [1,10,100,1000]
+        tofilename :: Int -> String
+        tofilename i = tempdir ++ "/temp" ++ show i
+    forM_ indexes $ \l -> writeFile (tofilename l) (show l)
+    let q l = lazyQuery cache (tofilename l) (computation (tofilename l))
+        qf l = lazyQuery cache (tofilename l) (throwIO (AssertionFailed "fail"))
+        check x m = unless x (error m)
+    lst1 <- mapM q indexes
+    lst2 <- mapM qf indexes
+    check (lst1 == lst2) "Request result was not cached"
+    removeFile (tofilename 10)
+    threadDelay (1*10^(6 :: Int))
+    cacheInfo <- getCache cache
+    check (HM.size cacheInfo == 3) "Invalidation didn't work"
+