diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,8 @@
+## 0.1.7
+
+* Support for ghc8
+* Simplify Sandbox-Monad
+
 ## 0.1.6
 
 * Support for HUnit>=1.5
diff --git a/src/Test/Sandbox/Internals.hs b/src/Test/Sandbox/Internals.hs
--- a/src/Test/Sandbox/Internals.hs
+++ b/src/Test/Sandbox/Internals.hs
@@ -15,18 +15,16 @@
 import Control.Concurrent
 import Control.Exception.Lifted hiding (throwTo)
 import Control.Monad
-import Control.Monad.Base (MonadBase)
 #if MIN_VERSION_mtl(2,2,1)
-import Control.Monad.Except (MonadError, catchError, throwError)
+import Control.Monad.Except (catchError, throwError)
 import Control.Monad.Trans.Except (ExceptT, runExceptT)
 #else
-import Control.Monad.Error (MonadError, catchError, throwError)
+import Control.Monad.Error (catchError, throwError)
 import Control.Monad.Trans.Error (ErrorT, runErrorT)
 #endif
 import Control.Monad.Loops
-import Control.Monad.Reader (MonadReader, ask)
-import Control.Monad.Trans (MonadIO, liftIO)
-import Control.Monad.Trans.Control (MonadBaseControl (..))
+import Control.Monad.Reader (ask)
+import Control.Monad.Trans (liftIO)
 import Control.Monad.Trans.Reader (ReaderT, runReaderT)
 import Data.ByteString (ByteString)
 import qualified Data.ByteString.Char8 as B
@@ -57,39 +55,13 @@
 import System.Random.Shuffle
 import Test.Sandbox.Process
 
-#if MIN_VERSION_mtl(2,2,1)
-type ExceptT' = ExceptT
-runExceptT' :: ExceptT e m a -> m (Either e a)
-runExceptT' = runExceptT
-#else
-runExceptT' :: ErrorT e m a -> m (Either e a)
-type ExceptT' = ErrorT
-runExceptT' = runErrorT
-#endif
-
-
 type Port = Int
 type SandboxStateRef = IORef SandboxState
 
-newtype Sandbox a = Sandbox {
-    runSB :: ExceptT' String (ReaderT SandboxStateRef IO) a
-  } deriving (Applicative, Functor, Monad, MonadBase IO, MonadError String, MonadReader (IORef SandboxState), MonadIO)
-
-#if MIN_VERSION_monad_control(1,0,0)
-newtype StMSandbox a = StMSandbox { runStMSandbox :: StM (ExceptT' String (ReaderT SandboxStateRef IO)) a }
-#endif
-
-instance MonadBaseControl IO Sandbox where
-#if MIN_VERSION_monad_control(1,0,0)
-  type StM Sandbox a = StMSandbox a
-#else
-  newtype StM Sandbox a = StMSandbox { runStMSandbox :: StM (ExceptT' String (ReaderT SandboxStateRef IO)) a }
-#endif
-  liftBaseWith f = Sandbox . liftBaseWith $ \run -> f (liftM StMSandbox . run . runSB)
-  restoreM = Sandbox . restoreM . runStMSandbox
+type Sandbox = ExceptT String (ReaderT SandboxStateRef IO)
 
 runSandbox :: Sandbox a -> SandboxStateRef -> IO (Either String a)
-runSandbox = runReaderT . runExceptT' . runSB
+runSandbox = runReaderT . runExceptT
 
 errorHandler :: String -> IO a
 errorHandler error' = do
@@ -497,10 +469,14 @@
 tryBinary :: FilePath -> IO (Maybe FilePath)
 tryBinary path = do
   expandedPath <- expand path
-  canonicalizedPath <- tryIOError $ D.canonicalizePath expandedPath
-  case canonicalizedPath of
-    Left _ -> D.findExecutable expandedPath
-    Right realPath -> D.findExecutable realPath
+  mexe <- D.findExecutable expandedPath
+  case mexe of
+    Nothing -> return Nothing
+    Just path' -> do
+      canonicalizedPath <- tryIOError $ D.canonicalizePath path'
+      case canonicalizedPath of
+        Left _ -> return Nothing
+        Right realPath -> return $ Just realPath
 
 getProcessCandidateBinaries :: SandboxedProcess -> [FilePath]
 getProcessCandidateBinaries sp =
diff --git a/test-sandbox.cabal b/test-sandbox.cabal
--- a/test-sandbox.cabal
+++ b/test-sandbox.cabal
@@ -1,5 +1,5 @@
 Name:           test-sandbox
-Version:        0.1.6
+Version:        0.1.7
 Cabal-Version:  >= 1.14
 Category:       Testing
 Synopsis:       Sandbox for system tests
@@ -28,7 +28,7 @@
 Source-Repository this
     Type:       git
     Location:   https://github.com/gree/haskell-test-sandbox
-    Tag:        test-sandbox_0.1.6
+    Tag:        test-sandbox_0.1.7
 
 Library
     Exposed-modules:    Test.Sandbox
@@ -51,8 +51,8 @@
                       , random
                       , random-shuffle
                       , temporary
-                      , transformers             >= 0.2      && < 0.5
-                      , transformers-compat      >= 0.3      && < 0.5
+                      , transformers
+                      , transformers-compat
                       , transformers-base
                       , unix
                       , regex-posix
diff --git a/test/test.hs b/test/test.hs
--- a/test/test.hs
+++ b/test/test.hs
@@ -182,8 +182,12 @@
           liftIO $ threadDelay $ 1 * 1000 * 1000
           liftIO $ (length pids >= 4) `shouldBe` True
         ref' <- readIORef val
-        pids <- runSandbox' ref' $ I.getAvailablePids
-        length pids `shouldBe` 0
+        let chkpid  :: IO Int
+            chkpid = do
+              threadDelay (5 * 1000 * 1000)
+              pids <- runSandbox' ref' $ I.getAvailablePids
+              return $ length pids
+        chkpid `shouldReturn` 0
 
       it "send kill signal for process groups" $ do
         sandbox "test" $ do