diff --git a/CmdLine.hs b/CmdLine.hs
index 8cf4d0544d..83a89ef7db 100644
--- a/CmdLine.hs
+++ b/CmdLine.hs
@@ -17,7 +17,7 @@ import qualified Control.Exception as E
 import qualified Data.Map as M
 import Control.Exception (throw)
 import System.Console.GetOpt
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 import System.Posix.Signals
 #endif
 
@@ -123,7 +123,7 @@ tryRun' errnum state cmd (a:as) = do
 {- Actions to perform each time ran. -}
 startup :: Annex Bool
 startup = liftIO $ do
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	void $ installHandler sigINT Default Nothing
 #endif
 	return True
diff --git a/Creds.hs b/Creds.hs
index 1b62c93400..9606a73d6f 100644
--- a/Creds.hs
+++ b/Creds.hs
@@ -107,7 +107,7 @@ getEnvCredPair storage = liftM2 (,)
 
 {- Stores a CredPair in the environment. -}
 setEnvCredPair :: CredPair -> CredPairStorage -> IO ()
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 setEnvCredPair (l, p) storage = do
 	set uenv l
 	set penv p
diff --git a/Git.hs b/Git.hs
index e14f4ec3a0..513f052a3e 100644
--- a/Git.hs
+++ b/Git.hs
@@ -32,7 +32,7 @@ module Git (
 ) where
 
 import Network.URI (uriPath, uriScheme, unEscapeString)
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 import System.Posix.Files
 #endif
 
@@ -131,7 +131,7 @@ hookPath script repo = do
 	ifM (catchBoolIO $ isexecutable hook)
 		( return $ Just hook , return Nothing )
   where
-#if __WINDOWS__
+#if mingw32_HOST_OS
 	isexecutable f = doesFileExist f
 #else
 	isexecutable f = isExecutable . fileMode <$> getFileStatus f
diff --git a/GitAnnex.hs b/GitAnnex.hs
index 1f6b1c177e..9553f22774 100644
--- a/GitAnnex.hs
+++ b/GitAnnex.hs
@@ -23,7 +23,7 @@ import qualified Command.Get
 import qualified Command.FromKey
 import qualified Command.DropKey
 import qualified Command.TransferKey
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 import qualified Command.TransferKeys
 #endif
 import qualified Command.ReKey
@@ -118,7 +118,7 @@ cmds = concat
 	, Command.FromKey.def
 	, Command.DropKey.def
 	, Command.TransferKey.def
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	, Command.TransferKeys.def
 #endif
 	, Command.ReKey.def
diff --git a/Init.hs b/Init.hs
index 25b83be499..7e7e5041d0 100644
--- a/Init.hs
+++ b/Init.hs
@@ -26,21 +26,23 @@ import qualified Annex.Branch
 import Logs.UUID
 import Annex.Version
 import Annex.UUID
-import Utility.UserInfo
 import Utility.Shell
-import Utility.FileMode
 import Config
 import Annex.Direct
 import Annex.Content.Direct
 import Annex.Environment
 import Backend
+#ifndef mingw32_HOST_OS
+import Utility.UserInfo
+import Utility.FileMode
+#endif
 
 genDescription :: Maybe String -> Annex String
 genDescription (Just d) = return d
 genDescription Nothing = do
 	reldir <- liftIO . relHome =<< fromRepo Git.repoPath
 	hostname <- fromMaybe "" <$> liftIO getHostname
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	let at = if null hostname then "" else "@"
 	username <- liftIO myUserName
 	return $ concat [username, at, hostname, ":", reldir]
@@ -129,7 +131,7 @@ preCommitScript = unlines
  - or removing write access from files. -}
 probeCrippledFileSystem :: Annex Bool
 probeCrippledFileSystem = do
-#ifdef __WINDOWS__
+#ifdef mingw32_HOST_OS
 	return True
 #else
 	tmp <- fromRepo gitAnnexTmpDir
@@ -177,7 +179,7 @@ checkCrippledFileSystem = whenM probeCrippledFileSystem $ do
 
 probeFifoSupport :: Annex Bool
 probeFifoSupport = do
-#ifdef __WINDOWS__
+#ifdef mingw32_HOST_OS
 	return False
 #else
 	tmp <- fromRepo gitAnnexTmpDir
diff --git a/Test.hs b/Test.hs
index 2adbb44c5a..5a869fa7c8 100644
--- a/Test.hs
+++ b/Test.hs
@@ -58,7 +58,7 @@ import qualified Utility.Env
 import qualified Utility.Gpg
 import qualified Utility.Matcher
 import qualified Utility.Exception
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 import qualified GitAnnex
 #endif
 
@@ -75,7 +75,7 @@ main = do
 	putStrLn "  (Do not be alarmed by odd output here; it's normal."
         putStrLn "   wait for the last line to see how it went.)"
 	rs <- runhunit =<< prepare False
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	directrs <- runhunit =<< prepare True
 #else
 	-- Windows is only going to use direct mode, so don't test twice.
@@ -221,7 +221,7 @@ test_add env = "git-annex add" ~: TestList [basic, sha1dup, subdirs]
 		git_annex env "add" ["dir"] @? "add of subdir failed"
 		createDirectory "dir2"
 		writeFile ("dir2" </> "foo") $ content annexedfile
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 		{- This does not work on Windows, for whatever reason. -}
 		setCurrentDirectory "dir"
 		git_annex env "add" [".." </> "dir2"] @? "add of ../subdir failed"
@@ -666,7 +666,7 @@ test_union_merge_regression env = "union merge regression" ~:
 						boolSystem "git" [Params "remote add r3", File ("../../" ++ r3)] @? "remote add"
 					git_annex env "get" [annexedfile] @? "get failed"
 					boolSystem "git" [Params "remote rm origin"] @? "remote rm"
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 				forM_ [r3, r2, r1] $ \r -> indir env r $
 					git_annex env "sync" [] @? "sync failed"
 				forM_ [r3, r2] $ \r -> indir env r $
@@ -707,7 +707,7 @@ test_conflict_resolution env = "automatic conflict resolution" ~:
 						git_annex env "unlock" [annexedfile] @? "unlock failed"		
 						writeFile annexedfile newcontent
 					)
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 			{- Sync twice in r1 so it gets the conflict resolution
 			 - update from r2 -}
 			forM_ [r1, r2, r1] $ \r -> indir env r $ do
@@ -761,7 +761,7 @@ test_whereis env = "git-annex whereis" ~: intmpclonerepo env $ do
 
 test_hook_remote :: TestEnv -> Test
 test_hook_remote env = "git-annex hook remote" ~: intmpclonerepo env $ do
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	git_annex env "initremote" (words "foo type=hook encryption=none hooktype=foo") @? "initremote failed"
 	createDirectory dir
 	git_config "annex.foo-store-hook" $
@@ -802,7 +802,7 @@ test_directory_remote env = "git-annex directory remote" ~: intmpclonerepo env $
 	annexed_present annexedfile
 	git_annex env "drop" [annexedfile, "--numcopies=2"] @? "drop failed"
 	annexed_notpresent annexedfile
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	-- moving from directory special remote fails on Windows TODO
 	git_annex env "move" [annexedfile, "--from", "foo"] @? "move --from directory remote failed"
 	annexed_present annexedfile
@@ -812,7 +812,7 @@ test_directory_remote env = "git-annex directory remote" ~: intmpclonerepo env $
 
 test_rsync_remote :: TestEnv -> Test
 test_rsync_remote env = "git-annex rsync remote" ~: intmpclonerepo env $ do
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	createDirectory "dir"
 	git_annex env "initremote" (words $ "foo type=rsync encryption=none rsyncurl=dir") @? "initremote failed"
 	git_annex env "get" [annexedfile] @? "get of file failed"
@@ -849,7 +849,7 @@ test_bup_remote env = "git-annex bup remote" ~: intmpclonerepo env $ when Build.
 -- gpg is not a build dependency, so only test when it's available
 test_crypto :: TestEnv -> Test
 test_crypto env = "git-annex crypto" ~: intmpclonerepo env $ whenM (Utility.Path.inPath Utility.Gpg.gpgcmd) $ do
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	Utility.Gpg.testTestHarness @? "test harness self-test failed"
 	Utility.Gpg.testHarness $ do
 		createDirectory "dir"
@@ -882,7 +882,7 @@ test_crypto env = "git-annex crypto" ~: intmpclonerepo env $ whenM (Utility.Path
 -- (when the OS allows) so test coverage collection works.
 git_annex :: TestEnv -> String -> [String] -> IO Bool
 git_annex env command params = do
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	forM_ (M.toList env) $ \(var, val) ->
 		Utility.Env.setEnv var val True
 
diff --git a/Upgrade.hs b/Upgrade.hs
index 30f2b7ed83..f0166bf8ef 100644
--- a/Upgrade.hs
+++ b/Upgrade.hs
@@ -11,7 +11,7 @@ module Upgrade where
 
 import Common.Annex
 import Annex.Version
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 import qualified Upgrade.V0
 import qualified Upgrade.V1
 #endif
@@ -20,7 +20,7 @@ import qualified Upgrade.V2
 upgrade :: Annex Bool
 upgrade = go =<< getVersion
   where
-#ifndef __WINDOWS__
+#ifndef mingw32_HOST_OS
 	go (Just "0") = Upgrade.V0.upgrade
 	go (Just "1") = Upgrade.V1.upgrade
 #else