diff --git a/Utility/FileIO.hs b/Utility/FileIO.hs
index 4b12b2ba0e..6a22025963 100644
--- a/Utility/FileIO.hs
+++ b/Utility/FileIO.hs
@@ -35,7 +35,9 @@ import System.File.OsPath
 -- https://github.com/haskell/file-io/issues/39
 import Utility.Path.Windows
 import Utility.OsPath
+import System.OsPath
 import System.IO (IO, Handle, IOMode)
+import Prelude (return)
 import qualified System.File.OsPath as O
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Lazy as L
@@ -84,7 +86,10 @@ appendFile' f b = do
 openTempFile :: OsPath -> OsPath -> IO (OsPath, Handle)
 openTempFile p s = do
 	p' <- toOsPath <$> convertToWindowsNativeNamespace (fromOsPath p)
-	O.openTempFile p' s
+	(t, h) <- O.openTempFile p' s
+	-- Avoid returning mangled path from convertToWindowsNativeNamespace
+	let t' = p </> takeFileName t
+	return (t', h)
 #endif
 
 #else
diff --git a/git-annex.cabal b/git-annex.cabal
index b610cdf65c..b662fe482e 100644
--- a/git-annex.cabal
+++ b/git-annex.cabal
@@ -333,14 +333,12 @@ Executable git-annex
       P2P.Http.State
 
   if flag(OsPath)
-    -- Currently this build flag does not pass the test suite on Windows
-    if (! os(windows))
-      Build-Depends:
-        os-string (>= 2.0.0),
-        directory (>= 1.3.8.3),
-        filepath (>= 1.5.2.0),
-        file-io (>= 0.1.3)
-      CPP-Options: -DWITH_OSPATH
+    Build-Depends:
+      os-string (>= 2.0.0),
+      directory (>= 1.3.8.3),
+      filepath (>= 1.5.2.0),
+      file-io (>= 0.1.3)
+    CPP-Options: -DWITH_OSPATH
 
   if (os(windows))
     Build-Depends: