diff --git a/Commands.hs b/Commands.hs
--- a/Commands.hs
+++ b/Commands.hs
@@ -38,12 +38,11 @@
 installed _ _ opts = do
     let optall = OptAll `elem` opts
         optrec = OptRecursive `elem` opts
-    flt <- if optall then allPkgs else userPkgs
     db' <- getPkgDB (getSandbox opts)
+    flt <- if optall then allPkgs else userPkgs
+    -- FIXME: the optall case does unnecessary conversion
     let pkgs = toPkgList flt db'
-    db <- if optall
-          then return db'
-          else toPkgDB . flip toPkgList db' <$> userPkgs
+        db = toPkgDB pkgs
     forM_ pkgs $ \pkg -> do
         putStrLn . fullNameOfPkgInfo $ pkg
         when optrec $ printDeps True db 1 pkg
diff --git a/Env.hs b/Env.hs
new file mode 100644
--- /dev/null
+++ b/Env.hs
@@ -0,0 +1,10 @@
+{-# LANGUAGE CPP #-}
+
+module Env (unsetEnv) where
+
+#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
+unsetEnv :: String -> IO ()
+unsetEnv _ = return ()
+#else
+import System.Posix.Env (unsetEnv)
+#endif
diff --git a/Main.hs b/Main.hs
--- a/Main.hs
+++ b/Main.hs
@@ -10,6 +10,7 @@
 import System.Console.GetOpt
 import System.Environment
 import System.Exit
+import Env
 import Types
 import Utils
 
@@ -17,6 +18,7 @@
 
 main :: IO ()
 main = flip catches handlers $ do
+    unsetEnv "GHC_PACKAGE_PATH"
     oargs <- getArgs
     let pargs = parseArgs getOptDB oargs
     checkOptions1 pargs illegalOptionsAndExit
diff --git a/Program.hs b/Program.hs
--- a/Program.hs
+++ b/Program.hs
@@ -1,7 +1,7 @@
 module Program where
 
 version :: String
-version = "0.1.1"
+version = "0.1.2"
 
 programName :: String
 programName = "cab"
diff --git a/cab.cabal b/cab.cabal
--- a/cab.cabal
+++ b/cab.cabal
@@ -1,5 +1,5 @@
 Name:                   cab
-Version:                0.1.1
+Version:                0.1.2
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -26,8 +26,13 @@
                         containers, Cabal,
                         attoparsec, attoparsec-enumerator,
                         enumerator, bytestring
+  if os(windows)
+     Build-Depends:
+  else
+     Build-Depends:     unix
   Other-Modules:	CmdDB
                         Commands
+                        Env
                         PkgDB
                         Process
                         Program