diff --git a/shake.cabal b/shake.cabal
--- a/shake.cabal
+++ b/shake.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.8
 build-type:         Simple
 name:               shake
-version:            0.3.6
+version:            0.3.7
 license:            BSD3
 license-file:       LICENSE
 category:           Development
@@ -127,6 +127,12 @@
         random,
         transformers >= 0.2 && < 0.4,
         deepseq >= 1.1 && < 1.4
+
+    if flag(portable)
+        cpp-options: -DPORTABLE
+    else
+        if !os(windows)
+            build-depends: unix >= 2.5.1
 
     other-modules:
         Examples.Util