diff --git a/Stackage/CheckPlan.hs b/Stackage/CheckPlan.hs
index 3f067f0d..8a6c9c42 100644
--- a/Stackage/CheckPlan.hs
+++ b/Stackage/CheckPlan.hs
@@ -2,25 +2,37 @@ module Stackage.CheckPlan
     ( checkPlan
     ) where
 
-import           Control.Monad        (unless)
-import           Data.List            (sort)
+import           Control.Monad        (unless, when)
+import           Data.List            (isPrefixOf, sort)
+import qualified Data.Map             as Map
+import qualified Data.Set             as Set
 import           Stackage.InstallInfo
 import           Stackage.Types
-import           System.Exit          (ExitCode (ExitFailure), exitWith)
-import           System.Process       (readProcess)
+import           Stackage.Util
+import           System.Exit          (ExitCode (ExitFailure, ExitSuccess),
+                                       exitWith)
+import           System.Process       (readProcessWithExitCode)
 
 data Mismatch = OnlyDryRun String | OnlySimpleList String
     deriving Show
 
 checkPlan :: InstallInfo -> IO ()
 checkPlan ii = do
-    dryRun' <- readProcess "cabal-dev" ("install":"--dry-run":"-fnetwork23":iiPackageList ii) ""
-    let dryRun = sort $ drop 2 $ lines dryRun'
-    let mismatches = getMismatches dryRun (iiPackageList ii)
+    (ec, dryRun', stderr) <- readProcessWithExitCode "cabal-dev" ("install":"--dry-run":"-fnetwork23":iiPackageList ii) ""
+    when (ec /= ExitSuccess || "Warning:" `isPrefixOf` stderr) $ do
+        putStr stderr
+        putStr dryRun'
+        putStrLn "cabal-dev returned a bad result, exiting"
+        exitWith ec
+    let dryRun = sort $ filter notOptionalCore $ map (takeWhile (/= ' ')) $ drop 2 $ lines dryRun'
+    let mismatches = getMismatches dryRun (filter notOptionalCore $ iiPackageList ii)
     unless (null mismatches) $ do
         putStrLn "Found the following mismtaches"
         mapM_ print mismatches
         exitWith $ ExitFailure 1
+  where
+    optionalCore = Set.fromList $ map packageVersionString $ Map.toList $ iiOptionalCore ii
+    notOptionalCore s = not $ s `Set.member` optionalCore
 
 getMismatches :: [String] -> [String] -> [Mismatch]
 getMismatches =
diff --git a/Stackage/Config.hs b/Stackage/Config.hs
index d4fb84fd..80893b6c 100644
--- a/Stackage/Config.hs
+++ b/Stackage/Config.hs
@@ -1,11 +1,9 @@
 {-# LANGUAGE CPP #-}
 module Stackage.Config where
 
-import           Control.Monad              (unless, when)
 import           Control.Monad.Trans.Writer (execWriter, tell)
 import qualified Data.Map                   as Map
 import           Data.Set                   (fromList, singleton)
-import           Distribution.System        (OS (..), buildOS)
 import           Distribution.Text          (simpleParse)
 import           Stackage.Types
 
diff --git a/Stackage/InstallInfo.hs b/Stackage/InstallInfo.hs
index d5a4d29c..b3116a5b 100644
--- a/Stackage/InstallInfo.hs
+++ b/Stackage/InstallInfo.hs
@@ -28,6 +28,7 @@ getInstallInfo = do
     return InstallInfo
         { iiCore = totalCore
         , iiPackages = Map.map fst final
+        , iiOptionalCore = Map.fromList $ map (\(PackageIdentifier p v) -> (p, v)) $ Set.toList $ hplibs hp
         }
 
 showDep :: (PackageName, (Version, [PackageName])) -> String
diff --git a/Stackage/LoadDatabase.hs b/Stackage/LoadDatabase.hs
index 61257027..64064b2b 100644
--- a/Stackage/LoadDatabase.hs
+++ b/Stackage/LoadDatabase.hs
@@ -1,7 +1,6 @@
 module Stackage.LoadDatabase where
 
 import qualified Codec.Archive.Tar                     as Tar
-import           Control.Exception                     (throwIO)
 import qualified Data.ByteString.Lazy                  as L
 import qualified Data.ByteString.Lazy.Char8            as L8
 import qualified Data.Map                              as Map
diff --git a/Stackage/Tarballs.hs b/Stackage/Tarballs.hs
index 32d7f21a..7cd1b3be 100644
--- a/Stackage/Tarballs.hs
+++ b/Stackage/Tarballs.hs
@@ -3,7 +3,6 @@ module Stackage.Tarballs
     ) where
 
 import qualified Codec.Archive.Tar       as Tar
-import           Control.Exception       (throwIO)
 import qualified Data.ByteString.Lazy    as L
 import qualified Data.Map                as Map
 import qualified Data.Set                as Set
diff --git a/Stackage/Types.hs b/Stackage/Types.hs
index 0fecab02..a9d18bc9 100644
--- a/Stackage/Types.hs
+++ b/Stackage/Types.hs
@@ -42,4 +42,8 @@ instance Monoid HaskellPlatform where
 data InstallInfo = InstallInfo
     { iiCore     :: Set PackageName
     , iiPackages :: Map PackageName Version
+    , iiOptionalCore :: Map PackageName Version
+      -- ^ This is intended to hold onto packages which might be automatically
+      -- provided in the global package database. In practice, this would be
+      -- Haskell Platform packages provided by distributions.
     }