diff --git a/CHANGES.txt b/CHANGES.txt
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,7 @@
 Changelog for Weeder
 
+0.1.9, released 2017-12-07
+    Don't report Win32/unix as unused on the alternate platform
 0.1.8, released 2017-12-06
     Follow both branches for if/else containing dependencies/modules
 0.1.7, released 2017-08-09
diff --git a/src/Check.hs b/src/Check.hs
--- a/src/Check.hs
+++ b/src/Check.hs
@@ -8,6 +8,7 @@
 import Data.Maybe
 import Data.List.Extra
 import Data.Tuple.Extra
+import System.Info.Extra
 import qualified Data.HashSet as Set
 import qualified Data.HashMap.Strict as Map
 import Warning
@@ -50,7 +51,8 @@
     [ Warning pkg [cabalSectionType] "Redundant build-depends entry" (Just p) Nothing Nothing
     | (CabalSection{..}, (x1,x2)) <- sections
     , let usedPackages = Set.unions $ map (Set.map fst . hiImportPackageModule . hi) $ x1 ++ x2
-    , p <- Set.toList $ Set.fromList cabalPackages `Set.difference` usedPackages]
+    , p <- Set.toList $ Set.fromList cabalPackages `Set.difference` usedPackages
+    , p /= if isWindows then "unix" else "Win32"] -- ignore packages that must be conditional on the other platform
 
 
 warnIncorrectOtherModules :: S -> [Warning]
diff --git a/weeder.cabal b/weeder.cabal
--- a/weeder.cabal
+++ b/weeder.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.18
 build-type:         Simple
 name:               weeder
-version:            0.1.8
+version:            0.1.9
 license:            BSD3
 license-file:       LICENSE
 category:           Development