diff --git a/cabal-sort.cabal b/cabal-sort.cabal
--- a/cabal-sort.cabal
+++ b/cabal-sort.cabal
@@ -1,6 +1,6 @@
 Cabal-Version:    2.2
 Name:             cabal-sort
-Version:          0.1.1
+Version:          0.1.1.1
 License:          BSD-3-Clause
 License-File:     LICENSE
 Author:           Henning Thielemann <haskell@henning-thielemann.de>
@@ -90,7 +90,7 @@
 Source-Repository this
   type:     darcs
   location: http://code.haskell.org/~thielema/cabal-sort/
-  tag:      0.1.1
+  tag:      0.1.1.1
 
 
 Executable cabal-sort
diff --git a/src/CabalSort.hs b/src/CabalSort.hs
--- a/src/CabalSort.hs
+++ b/src/CabalSort.hs
@@ -24,6 +24,7 @@
 import qualified Control.Monad.Trans.Class as Trans
 import Control.Arrow ((***))
 import Control.Monad (guard, when)
+import Control.Applicative (pure, (<*>), (<|>))
 
 import qualified Data.List as List
 import qualified Data.Map as Map
@@ -43,8 +44,7 @@
    Flags {
       optVerbosity :: Verbosity.Verbosity,
       optInfo :: SourcePackage -> String,
-      optParallel :: Bool,
-      optMakefile :: Bool,
+      optOutputFormat :: Format,
       optBuilddir :: FilePath,
       optInstall  :: String
    }
@@ -67,6 +67,9 @@
       ("dir", FilePath.takeDirectory . location) :
       []
 
+data Format = Serial | Parallel | Makefile
+   deriving (Eq, Ord, Show, Enum)
+
 options :: OP.Parser Flags
 options =
    pure Flags
@@ -89,15 +92,15 @@
           OP.help ("kind of output: " ++
                      List.intercalate ", " (Map.keys infoMap)))
    <*>
-      OP.switch
-         (OP.short 'p' <>
-          OP.long "parallel" <>
-          OP.help "Display independently buildable groups of packages")
-   <*>
-      OP.switch
+      (OP.flag' Makefile
          (OP.short 'm' <>
           OP.long "makefile" <>
           OP.help "Generate a makefile of package dependencies")
+       <|>
+       OP.flag Serial Parallel
+         (OP.short 'p' <>
+          OP.long "parallel" <>
+          OP.help "Display independently buildable groups of packages"))
    <*>
       OP.strOption
          (OP.long "builddir" <>
@@ -141,15 +144,13 @@
           graph = getBuildGraph pkgs
       checkForCycles graph
       Trans.lift $
-         if optMakefile flags
-           then printMakefile flags $ getDeps graph
-           else if optParallel flags
-              then
+         case optOutputFormat flags of
+            Makefile -> printMakefile flags $ getDeps graph
+            Serial -> mapM_ (putStrLn . optInfo flags) $ topsort' graph
+            Parallel ->
                  mapM_ (putStrLn . unwords . map (optInfo flags)) $
                  map (topsort' . subgraph graph) $
                  components graph
-              else
-                 mapM_ (putStrLn . optInfo flags) $ topsort' graph
 
 
 printMakefile :: Flags -> [(SourcePackage, [SourcePackage])] -> IO ()
@@ -181,9 +182,7 @@
                   (Graph.pre gr . Graph.node' $ ctx))
     in  Graph.ufold (\ctx ds -> c2dep ctx : ds) [] gr
 
-getBuildGraph ::
-   [SourcePackage] ->
-   Gr SourcePackage ()
+getBuildGraph :: [SourcePackage] -> Gr SourcePackage ()
 getBuildGraph srcPkgs =
    let nodes = zip [0..] srcPkgs
        nodeDict =
@@ -216,8 +215,7 @@
 
 nodeLabels :: Gr a b -> [Graph.Node] -> [a]
 nodeLabels graph =
-   map (fromMaybe (error "node not found in graph") .
-        Graph.lab graph)
+   map (fromMaybe (error "node not found in graph") . Graph.lab graph)
 
 subgraph :: Gr a b -> [Graph.Node] -> Gr a b
 subgraph graph nodes =