diff --git a/ghcup.cabal b/ghcup.cabal
index 2565d7a..ff65ac7 100644
--- a/ghcup.cabal
+++ b/ghcup.cabal
@@ -431,6 +431,9 @@ test-suite ghcup-optparse-test
     Utils
     WhereisTest
 
+  if os(windows)
+    cpp-options: -DIS_WINDOWS
+
   default-language: Haskell2010
   ghc-options:      -Wall
   build-depends:
diff --git a/test/optparse-test/CompileTest.hs b/test/optparse-test/CompileTest.hs
index 9979a9e..e246757 100644
--- a/test/optparse-test/CompileTest.hs
+++ b/test/optparse-test/CompileTest.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE CPP #-}
 
 module CompileTest where
 
@@ -91,8 +92,13 @@ compileGhcCheckList = mapSecond CompileGHC
   , (baseCmd <> "--flavour make", baseOptions{GHC.buildFlavour = Just "make"})
   , (baseCmd <> "--hadrian", baseOptions{GHC.buildSystem = Just Hadrian})
   , (baseCmd <> "--make", baseOptions{GHC.buildSystem = Just Make})
+#ifdef IS_WINDOWS
+  , (baseCmd <> "-i C:\\\\tmp\\out_dir", baseOptions{GHC.isolateDir = Just "C:\\\\tmp\\out_dir"})
+  , (baseCmd <> "--isolate C:\\\\tmp\\out_dir", baseOptions{GHC.isolateDir = Just "C:\\\\tmp\\out_dir"})
+#else
   , (baseCmd <> "-i /tmp/out_dir", baseOptions{GHC.isolateDir = Just "/tmp/out_dir"})
   , (baseCmd <> "--isolate /tmp/out_dir", baseOptions{GHC.isolateDir = Just "/tmp/out_dir"})
+#endif
   ]
   where
     baseCmd :: String
@@ -150,8 +156,13 @@ compileHlsCheckList = mapSecond CompileHLS
   , (baseCmd <> "-o 2.0.0.0-p1", baseOptions{HLS.ovewrwiteVer = Right $ mkVersion' "2.0.0.0-p1"})
   , (baseCmd <> "--overwrite-version 2.0.0.0-p1", baseOptions{HLS.ovewrwiteVer = Right $ mkVersion' "2.0.0.0-p1"})
   , (baseCmd <> "--git-describe-version", baseOptions{HLS.ovewrwiteVer = Left True})
+#ifdef IS_WINDOWS
+  , (baseCmd <> "-i C:\\\\tmp\\out_dir", baseOptions{HLS.isolateDir = Just "C:\\\\tmp\\out_dir"})
+  , (baseCmd <> "--isolate C:\\\\tmp\\out_dir", baseOptions{HLS.isolateDir = Just "C:\\\\tmp\\out_dir"})
+#else
   , (baseCmd <> "-i /tmp/out_dir", baseOptions{HLS.isolateDir = Just "/tmp/out_dir"})
   , (baseCmd <> "--isolate /tmp/out_dir", baseOptions{HLS.isolateDir = Just "/tmp/out_dir"})
+#endif
   , (baseCmd <> "--cabal-project file:///tmp/cabal.project", baseOptions{HLS.cabalProject = Just $ Right [uri|file:///tmp/cabal.project|]})
   , (baseCmd <> "--cabal-project cabal.ghc8107.project", baseOptions{HLS.cabalProject = Just $ Left "cabal.ghc8107.project"})
   , (baseCmd <> "--cabal-project-local file:///tmp/cabal.project.local", baseOptions{HLS.cabalProjectLocal = Just [uri|file:///tmp/cabal.project.local|]})
diff --git a/test/optparse-test/InstallTest.hs b/test/optparse-test/InstallTest.hs
index 5dcfe35..8f13e42 100644
--- a/test/optparse-test/InstallTest.hs
+++ b/test/optparse-test/InstallTest.hs
@@ -1,5 +1,6 @@
+{-# LANGUAGE CPP               #-}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE QuasiQuotes       #-}
 
 module InstallTest where
 
@@ -45,7 +46,11 @@ oldStyleCheckList =
       ("install", Right defaultOptions)
     : ("install --set", Right defaultOptions{instSet = True})
     : ("install --force", Right defaultOptions{forceInstall = True})
+#ifdef IS_WINDOWS
+    : ("install -i C:\\\\", Right defaultOptions{Install.isolateDir = Just "C:\\\\"})
+#else
     : ("install -i /", Right defaultOptions{Install.isolateDir = Just "/"})
+#endif
     : ("install -u https://gitlab.haskell.org/ghc/ghc/-/jobs/artifacts/master/raw/ghc-x86_64-linux-fedora33-release.tar.xz head"
     , Right defaultOptions
         { instBindist = Just [uri|https://gitlab.haskell.org/ghc/ghc/-/jobs/artifacts/master/raw/ghc-x86_64-linux-fedora33-release.tar.xz|]
diff --git a/test/optparse-test/RunTest.hs b/test/optparse-test/RunTest.hs
index f32f25e..d5c4a94 100644
--- a/test/optparse-test/RunTest.hs
+++ b/test/optparse-test/RunTest.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE CPP               #-}
 
 module RunTest where
 
@@ -39,8 +40,13 @@ runCheckList =
   , ("run --cabal 3.10", defaultOptions{runCabalVer = Just $ ToolVersion $ mkVersion' "3.10"})
   , ("run --hls 2.0", defaultOptions{runHLSVer = Just $ ToolVersion $ mkVersion' "2.0"})
   , ("run --stack 2.9", defaultOptions{runStackVer = Just $ ToolVersion $ mkVersion' "2.9"})
+#ifdef IS_WINDOWS
+  , ("run -b C:\\\\tmp\\dir", defaultOptions{runBinDir = Just "C:\\\\tmp\\dir"})
+  , ("run --bindir C:\\\\tmp\\dir", defaultOptions{runBinDir = Just "C:\\\\tmp\\dir"})
+#else
   , ("run -b /tmp/dir", defaultOptions{runBinDir = Just "/tmp/dir"})
   , ("run --bindir /tmp/dir", defaultOptions{runBinDir = Just "/tmp/dir"})
+#endif
   , ("run -q", defaultOptions{runQuick = True})
   , ("run --quick", defaultOptions{runQuick = True})
   , ("run --ghc latest --cabal 3.10 --stack 2.9 --hls 2.0 --install",