diff --git a/Main.hs b/Main.hs
--- a/Main.hs
+++ b/Main.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 module Main (main) where
 
 import Control.Applicative
@@ -6,6 +8,7 @@
 import Data.List
 import Data.Monoid
         ( Monoid(..) )
+import qualified Data.Semigroup as S
 
 -- cabal
 import Distribution.Simple.Setup
@@ -36,6 +39,8 @@
 import System.Environment ( getArgs, getProgName )
 import System.Directory ( doesDirectoryExist )
 import System.Exit ( exitFailure )
+{-# LANGUAGE CPP #-}
+
 import System.FilePath ( (</>) )
 
 import qualified HackPort.GlobalFlags as H
@@ -56,14 +61,24 @@
     listVerbosity :: Flag Verbosity
   }
 
+#if MIN_VERSION_base(4,9,0)
+instance S.Semigroup ListFlags where
+  a <> b = ListFlags {
+    listVerbosity = combine listVerbosity
+  }
+    where combine field = field a S.<> field b
+#endif
+
 instance Monoid ListFlags where
   mempty = ListFlags {
     listVerbosity = mempty
   }
+#if !(MIN_VERSION_base(4,11,0))
   mappend a b = ListFlags {
     listVerbosity = combine listVerbosity
   }
     where combine field = field a `mappend` field b
+#endif
 
 defaultListFlags :: ListFlags
 defaultListFlags = ListFlags {
@@ -119,16 +134,27 @@
   , makeEbuildCabalFlags :: Flag (Maybe String)
   }
 
+#if MIN_VERSION_base(4,9,0)
+instance S.Semigroup MakeEbuildFlags where
+  a <> b = MakeEbuildFlags {
+    makeEbuildVerbosity = combine makeEbuildVerbosity
+  , makeEbuildCabalFlags = makeEbuildCabalFlags b
+  }
+    where combine field = field a S.<> field b
+#endif
+
 instance Monoid MakeEbuildFlags where
   mempty = MakeEbuildFlags {
     makeEbuildVerbosity = mempty
   , makeEbuildCabalFlags = mempty
   }
+#if MIN_VERSION_base(4,9,0)
   mappend a b = MakeEbuildFlags {
     makeEbuildVerbosity = combine makeEbuildVerbosity
   , makeEbuildCabalFlags = makeEbuildCabalFlags b
   }
     where combine field = field a `mappend` field b
+#endif
 
 defaultMakeEbuildFlags :: MakeEbuildFlags
 defaultMakeEbuildFlags = MakeEbuildFlags {
@@ -180,14 +206,24 @@
     updateVerbosity :: Flag Verbosity
   }
 
+#if MIN_VERSION_base(4,9,0)
+instance S.Semigroup UpdateFlags where
+  a <> b = UpdateFlags {
+    updateVerbosity = combine updateVerbosity
+  }
+    where combine field = field a S.<> field b
+#endif
+
 instance Monoid UpdateFlags where
   mempty = UpdateFlags {
     updateVerbosity = mempty
   }
+#if !(MIN_VERSION_base(4,11,0))
   mappend a b = UpdateFlags {
     updateVerbosity = combine updateVerbosity
   }
     where combine field = field a `mappend` field b
+#endif
 
 defaultUpdateFlags :: UpdateFlags
 defaultUpdateFlags = UpdateFlags {
@@ -284,16 +320,27 @@
   , mergeCabalFlags :: Flag (Maybe String)
   }
 
+#if MIN_VERSION_base(4,9,0)
+instance S.Semigroup MergeFlags where
+  a <> b = MergeFlags {
+    mergeVerbosity = combine mergeVerbosity
+  , mergeCabalFlags = mergeCabalFlags b
+  }
+    where combine field = field a S.<> field b
+#endif
+
 instance Monoid MergeFlags where
   mempty = MergeFlags {
     mergeVerbosity = mempty
   , mergeCabalFlags = mempty
   }
+#if !(MIN_VERSION_base(4,11,0))
   mappend a b = MergeFlags {
     mergeVerbosity = combine mergeVerbosity
   , mergeCabalFlags = mergeCabalFlags b
   }
     where combine field = field a `mappend` field b
+#endif
 
 defaultMergeFlags :: MergeFlags
 defaultMergeFlags = MergeFlags {
diff --git a/Merge/Dependencies.hs b/Merge/Dependencies.hs
--- a/Merge/Dependencies.hs
+++ b/Merge/Dependencies.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 {- | Merge a package from hackage to an ebuild.
  -}
 module Merge.Dependencies
@@ -32,6 +34,10 @@
 
 import Debug.Trace ( trace )
 
+#if MIN_VERSION_base(4,9,0)
+import Data.Semigroup (Semigroup(..))
+#endif
+
 -- | Dependencies of an ebuild
 data EDep = EDep
   {
@@ -42,6 +48,16 @@
   }
   deriving (Show, Eq, Ord)
 
+#if MIN_VERSION_base(4,9,0)
+instance Semigroup EDep where
+  (EDep rdepA rdep_eA depA dep_eA) <> (EDep rdepB rdep_eB depB dep_eB) = EDep
+    { rdep   = Portage.DependAllOf [rdepA, rdepB]
+    , rdep_e = rdep_eA `S.union` rdep_eB
+    , dep    = Portage.DependAllOf [depA, depB]
+    , dep_e  = dep_eA  `S.union` dep_eB
+    }
+#endif  
+  
 instance Monoid EDep where
   mempty = EDep
       {
@@ -50,12 +66,14 @@
         dep = Portage.empty_dependency,
         dep_e = S.empty
       }
+#if !(MIN_VERSION_base(4,11,0))
   (EDep rdepA rdep_eA depA dep_eA) `mappend` (EDep rdepB rdep_eB depB dep_eB) = EDep
     { rdep   = Portage.DependAllOf [rdepA, rdepB]
     , rdep_e = rdep_eA `S.union` rdep_eB
     , dep    = Portage.DependAllOf [depA, depB]
     , dep_e  = dep_eA  `S.union` dep_eB
     }
+#endif
 
 resolveDependencies :: Portage.Overlay -> Cabal.PackageDescription -> Cabal.CompilerInfo
                     -> [Cabal.PackageName] -> Cabal.PackageName
diff --git a/Portage/Dependency/Print.hs b/Portage/Dependency/Print.hs
--- a/Portage/Dependency/Print.hs
+++ b/Portage/Dependency/Print.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 module Portage.Dependency.Print
   (
     dep2str
@@ -11,7 +13,8 @@
 
 import qualified Distribution.Text as DT
 import qualified Text.PrettyPrint as Disp
-import Text.PrettyPrint ( (<>), vcat, nest, render )
+import Text.PrettyPrint ( vcat, nest, render )
+import Text.PrettyPrint as PP ((<>))
 
 import Portage.Dependency.Types
 
@@ -21,17 +24,17 @@
 dispSlot (GivenSlot slot) = Disp.text (':' : slot)
 
 dispLBound :: PackageName -> LBound -> Disp.Doc
-dispLBound pn (StrictLB    v) = Disp.char '>' <> DT.disp pn <-> DT.disp v
-dispLBound pn (NonstrictLB v) = Disp.text ">=" <> DT.disp pn <-> DT.disp v
+dispLBound pn (StrictLB    v) = Disp.char '>' PP.<> DT.disp pn <-> DT.disp v
+dispLBound pn (NonstrictLB v) = Disp.text ">=" PP.<> DT.disp pn <-> DT.disp v
 dispLBound _pn ZeroB = error "unhandled 'dispLBound ZeroB'"
 
 dispUBound :: PackageName -> UBound -> Disp.Doc
-dispUBound pn (StrictUB    v) = Disp.char '<' <> DT.disp pn <-> DT.disp v
-dispUBound pn (NonstrictUB v) = Disp.text "<=" <> DT.disp pn <-> DT.disp v
+dispUBound pn (StrictUB    v) = Disp.char '<' PP.<> DT.disp pn <-> DT.disp v
+dispUBound pn (NonstrictUB v) = Disp.text "<=" PP.<> DT.disp pn <-> DT.disp v
 dispUBound _pn InfinityB = error "unhandled 'dispUBound Infinity'"
 
 dispDAttr :: DAttr -> Disp.Doc
-dispDAttr (DAttr s u) = dispSlot s <> dispUses u
+dispDAttr (DAttr s u) = dispSlot s PP.<> dispUses u
 
 dep2str :: Int -> Dependency -> String
 dep2str start_indent = render . nest start_indent . showDepend
@@ -40,13 +43,13 @@
 dep2str_noindent = render . showDepend
 
 (<->) :: Disp.Doc -> Disp.Doc -> Disp.Doc
-a <-> b = a <> Disp.char '-' <> b
+a <-> b = a PP.<> Disp.char '-' PP.<> b
 
 sp :: Disp.Doc
 sp = Disp.char ' '
 
 sparens :: Disp.Doc -> Disp.Doc
-sparens doc = Disp.parens (sp <> valign doc <> sp)
+sparens doc = Disp.parens (sp PP.<> valign doc PP.<> sp)
 
 valign :: Disp.Doc -> Disp.Doc
 valign d = nest 0 d
@@ -55,24 +58,24 @@
 showDepend (DependAtom (Atom pn range dattr))
     = case range of
         -- any version
-        DRange ZeroB InfinityB -> DT.disp pn       <> dispDAttr dattr
-        DRange ZeroB ub        -> dispUBound pn ub <> dispDAttr dattr
-        DRange lb InfinityB    -> dispLBound pn lb <> dispDAttr dattr
+        DRange ZeroB InfinityB -> DT.disp pn       PP.<> dispDAttr dattr
+        DRange ZeroB ub        -> dispUBound pn ub PP.<> dispDAttr dattr
+        DRange lb InfinityB    -> dispLBound pn lb PP.<> dispDAttr dattr
         -- TODO: handle >=foo-0    special case
         -- TODO: handle =foo-x.y.* special case
         DRange lb ub          ->    showDepend (DependAtom (Atom pn (DRange lb InfinityB) dattr))
-                                 <> Disp.char ' '
-                                 <> showDepend (DependAtom (Atom pn (DRange ZeroB ub)    dattr))
-        DExact v              -> Disp.char '~' <> DT.disp pn <-> DT.disp v { versionRevision = 0 } <> dispDAttr dattr
+                                 PP.<> Disp.char ' '
+                                 PP.<> showDepend (DependAtom (Atom pn (DRange ZeroB ub)    dattr))
+        DExact v              -> Disp.char '~' PP.<> DT.disp pn <-> DT.disp v { versionRevision = 0 } PP.<> dispDAttr dattr
 
 showDepend (DependIfUse u td fd)  = valign $ vcat [td_doc, fd_doc]
     where td_doc
               | is_empty_dependency td = Disp.empty
-              | otherwise =                  DT.disp u <> Disp.char '?' <> sp <> sparens (showDepend td)
+              | otherwise =                  DT.disp u PP.<> Disp.char '?' PP.<> sp PP.<> sparens (showDepend td)
           fd_doc
               | is_empty_dependency fd = Disp.empty
-              | otherwise = Disp.char '!' <> DT.disp u <> Disp.char '?' <> sp <> sparens (showDepend fd)
-showDepend (DependAnyOf deps)   = Disp.text "||" <> sp <> sparens (vcat $ map showDependInAnyOf deps)
+              | otherwise = Disp.char '!' PP.<> DT.disp u PP.<> Disp.char '?' PP.<> sp PP.<> sparens (showDepend fd)
+showDepend (DependAnyOf deps)   = Disp.text "||" PP.<> sp PP.<> sparens (vcat $ map showDependInAnyOf deps)
 showDepend (DependAllOf deps)   = valign $ vcat $ map showDepend deps
 
 -- needs special grouping
diff --git a/Portage/PackageId.hs b/Portage/PackageId.hs
--- a/Portage/PackageId.hs
+++ b/Portage/PackageId.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 -- | Portage package identifiers, which unlike Cabal ones include a category.
 --
 module Portage.PackageId (
@@ -30,6 +32,10 @@
 
 import Distribution.Text(display)
 import System.FilePath ( (</>) )
+
+#if MIN_VERSION_base(4,11,0)
+import Prelude hiding ((<>))
+#endif
 
 newtype Category = Category { unCategory :: String }
   deriving (Eq, Ord, Show, Read)
diff --git a/Portage/Use.hs b/Portage/Use.hs
--- a/Portage/Use.hs
+++ b/Portage/Use.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 module Portage.Use (
   -- * main structures
   UseFlag(..),
@@ -12,6 +14,10 @@
 import qualified Text.PrettyPrint as Disp
 import Text.PrettyPrint ((<>))
 import qualified Distribution.Text as DT
+
+#if MIN_VERSION_base(4,11,0)
+import Prelude hiding ((<>))
+#endif
 
 -- | Use variable modificator
 data UseFlag = UseFlag Use           -- ^ no modificator
diff --git a/Portage/Version.hs b/Portage/Version.hs
--- a/Portage/Version.hs
+++ b/Portage/Version.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 {-|
     Author      :  Andres Loeh <kosmikus@gentoo.org>
     Stability   :  provisional
@@ -25,6 +27,10 @@
 import qualified Text.PrettyPrint as Disp
 import Text.PrettyPrint ((<>))
 import qualified Data.Char as Char (isAlpha, isDigit)
+
+#if MIN_VERSION_base(4,11,0)
+import Prelude hiding ((<>))
+#endif
 
 data Version = Version { versionNumber   :: [Int]         -- [1,42,3] ~= 1.42.3
                        , versionChar     :: (Maybe Char)  -- optional letter
diff --git a/hackport.cabal b/hackport.cabal
--- a/hackport.cabal
+++ b/hackport.cabal
@@ -1,5 +1,5 @@
 Name:           hackport
-Version:        0.5.5
+Version:        0.5.6
 License:        GPL
 License-file:   LICENSE
 Author:         Henning Günther, Duncan Coutts, Lennart Kolmodin