diff --git a/hoppy-generator.cabal b/hoppy-generator.cabal
--- a/hoppy-generator.cabal
+++ b/hoppy-generator.cabal
@@ -1,5 +1,5 @@
 name: hoppy-generator
-version: 0.5.0
+version: 0.5.1
 synopsis: C++ FFI generator - Code generator
 homepage: http://khumba.net/projects/hoppy
 license: AGPL-3
diff --git a/src/Foreign/Hoppy/Generator/Language/Haskell.hs b/src/Foreign/Hoppy/Generator/Language/Haskell.hs
--- a/src/Foreign/Hoppy/Generator/Language/Haskell.hs
+++ b/src/Foreign/Hoppy/Generator/Language/Haskell.hs
@@ -130,6 +130,7 @@
 #if !MIN_VERSION_base(4,8,0)
 import Data.Monoid (Monoid, mappend, mconcat, mempty)
 #endif
+import Data.Semigroup as Sem
 import qualified Data.Set as S
 import Data.Tuple (swap)
 import Foreign.Hoppy.Generator.Common
@@ -339,11 +340,14 @@
     -- whole module.
   }
 
+instance Sem.Semigroup Output where
+  (Output e i b x) <> (Output e' i' b' x') =
+    Output (e <> e') (i <> i') (b <> b') (x <> x')
+
 instance Monoid Output where
   mempty = Output mempty mempty mempty mempty
 
-  (Output e i b x) `mappend` (Output e' i' b' x') =
-    Output (e `mappend` e') (i `mappend` i') (b `mappend` b') (x `mappend` x')
+  mappend = (<>)
 
   mconcat os =
     Output (mconcat $ map outputExports os)
diff --git a/src/Foreign/Hoppy/Generator/Language/Haskell/Internal.hs b/src/Foreign/Hoppy/Generator/Language/Haskell/Internal.hs
--- a/src/Foreign/Hoppy/Generator/Language/Haskell/Internal.hs
+++ b/src/Foreign/Hoppy/Generator/Language/Haskell/Internal.hs
@@ -155,12 +155,22 @@
   -- GeneralizedNewtypeDeriving is to enable automatic deriving of
   -- Data.Bits.Bits instances for bitspace newtypes.
   concat
-  [ "{-# LANGUAGE CPP, FlexibleContexts, FlexibleInstances, GeneralizedNewtypeDeriving"
-  , ", MultiParamTypeClasses, ScopedTypeVariables, TypeSynonymInstances, UndecidableInstances #-}\n"
+  [ concat $ "{-# LANGUAGE " : intersperse ", " extensions ++ [" #-}\n"]
   , "#if !MIN_VERSION_base(4,8,0)\n"
   , "{-# LANGUAGE OverlappingInstances #-}\n"
   , "#endif\n\n"
   ]
+  where extensions =
+          [ "CPP"
+          , "FlexibleContexts"
+          , "FlexibleInstances"
+          , "ForeignFunctionInterface"
+          , "GeneralizedNewtypeDeriving"
+          , "MultiParamTypeClasses"
+          , "ScopedTypeVariables"
+          , "TypeSynonymInstances"
+          , "UndecidableInstances"
+          ]
 
 generateSource :: Module -> Generator ()
 generateSource m = do
diff --git a/src/Foreign/Hoppy/Generator/Spec/Base.hs b/src/Foreign/Hoppy/Generator/Spec/Base.hs
--- a/src/Foreign/Hoppy/Generator/Spec/Base.hs
+++ b/src/Foreign/Hoppy/Generator/Spec/Base.hs
@@ -218,6 +218,7 @@
 #if !MIN_VERSION_base(4,8,0)
 import Data.Monoid (Monoid, mappend, mconcat, mempty)
 #endif
+import Data.Semigroup as Sem
 import qualified Data.Set as S
 import Foreign.Hoppy.Generator.Common
 import {-# SOURCE #-} qualified Foreign.Hoppy.Generator.Language.Haskell as Haskell
@@ -581,10 +582,13 @@
     -- ^ The includes specified by a 'Reqs'.
   } deriving (Show)
 
+instance Sem.Semigroup Reqs where
+  (<>) (Reqs incl) (Reqs incl') = Reqs $ mappend incl incl'
+
 instance Monoid Reqs where
   mempty = Reqs mempty
 
-  mappend (Reqs incl) (Reqs incl') = Reqs $ mappend incl incl'
+  mappend = (<>)
 
   mconcat reqs = Reqs $ mconcat $ map reqsIncludes reqs
 
@@ -636,7 +640,7 @@
 newtype ExtName = ExtName
   { fromExtName :: String
     -- ^ Returns the string an an 'ExtName' contains.
-  } deriving (Eq, Monoid, Ord)
+  } deriving (Eq, Sem.Semigroup, Monoid, Ord)
 
 instance Show ExtName where
   show extName = concat ["$\"", fromExtName extName, "\"$"]
@@ -2290,11 +2294,14 @@
     -- ^ Extracts the list of exception handlers.
   }
 
+instance Sem.Semigroup ExceptionHandlers where
+  (<>) e1 e2 =
+    ExceptionHandlers $ exceptionHandlersList e1 ++ exceptionHandlersList e2
+
 instance Monoid ExceptionHandlers where
   mempty = ExceptionHandlers []
 
-  mappend e1 e2 =
-    ExceptionHandlers $ exceptionHandlersList e1 ++ exceptionHandlersList e2
+  mappend = (<>)
 
 -- | Types that can handle exceptions.
 class HandlesExceptions a where
@@ -2318,9 +2325,12 @@
     -- exports.
   }
 
+instance Sem.Semigroup Addendum where
+  (<>) (Addendum a) (Addendum b) = Addendum $ a >> b
+
 instance Monoid Addendum where
   mempty = Addendum $ return ()
-  mappend (Addendum a) (Addendum b) = Addendum $ a >> b
+  mappend = (<>)
 
 -- | A typeclass for types that have an addendum.
 class HasAddendum a where
@@ -2357,11 +2367,14 @@
     -- bindings.
   } deriving (Show)
 
+instance Sem.Semigroup HsImportSet where
+  (<>) (HsImportSet m) (HsImportSet m') =
+    HsImportSet $ M.unionWith mergeImportSpecs m m'
+
 instance Monoid HsImportSet where
   mempty = HsImportSet M.empty
 
-  mappend (HsImportSet m) (HsImportSet m') =
-    HsImportSet $ M.unionWith mergeImportSpecs m m'
+  mappend = (<>)
 
   mconcat sets =
     HsImportSet $ M.unionsWith mergeImportSpecs $ map getHsImportSet sets