diff --git a/unix.cabal b/unix.cabal
index 0ae27728820832f599dd42e45df47cad49b3ab7d..cbe3716fe6cdc18f34e337ee453938db41502d87 100644
--- a/unix.cabal
+++ b/unix.cabal
@@ -49,14 +49,16 @@ library
         DeriveDataTypeable
         InterruptibleFFI
         NondecreasingIndentation
-        OverloadedStrings
         RankNTypes
         RecordWildCards
-
-    if impl(ghc)
-        other-extensions:
-            Safe
-            Trustworthy
+        Safe
+        Trustworthy
+
+    if os(windows)
+        -- This package currently supports neither Cygwin nor MinGW,
+        -- therefore os(windows) is effectively not supported.
+        build-depends: unbuildable<0
+        buildable: False
 
     build-depends:
         base        >= 4.5     && < 4.10,