diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## Changes in 0.28.1
+  - GHC 8.4.1 compatibility
+
 ## Changes in 0.28.0
   - Add support for `cxx-options` and `cxx-sources` (see #205)
   - Add support for `data-dir` (see #100)
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2014-2016 Simon Hengel <sol@typeful.net>
+Copyright (c) 2014-2018 Simon Hengel <sol@typeful.net>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/hpack.cabal b/hpack.cabal
--- a/hpack.cabal
+++ b/hpack.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: e6f8fbe41b4e0a521f34c4fea72bce81d6d2fbe27b00462a16c07b3b3d049d34
+-- hash: 7d11b64019bcd70a856a7bd339ef0a2be052be71eff6a5a81bd549cd56befe1c
 
 name:           hpack
-version:        0.28.0
+version:        0.28.1
 synopsis:       An alternative format for Haskell packages
 description:    See README at <https://github.com/sol/hpack#readme>
 category:       Development
diff --git a/src/Data/Aeson/Config/Types.hs b/src/Data/Aeson/Config/Types.hs
--- a/src/Data/Aeson/Config/Types.hs
+++ b/src/Data/Aeson/Config/Types.hs
@@ -4,7 +4,7 @@
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 module Data.Aeson.Config.Types where
 
-import           Data.Monoid hiding (Product)
+import           Data.Semigroup (Semigroup(..))
 import           Data.Bitraversable
 import           Data.Bifoldable
 import           Data.Bifunctor
@@ -12,7 +12,7 @@
 import           Data.Aeson.Config.FromValue
 
 newtype List a = List {fromList :: [a]}
-  deriving (Eq, Show, Functor, Foldable, Traversable, Monoid)
+  deriving (Eq, Show, Functor, Foldable, Traversable, Semigroup, Monoid)
 
 instance FromValue a => FromValue (List a) where
   fromValue v = List <$> case v of
@@ -25,9 +25,12 @@
 data Product a b = Product a b
   deriving (Eq, Show, Functor, Foldable, Traversable)
 
-instance (Monoid a, Monoid b) => Monoid (Product a b) where
+instance (Semigroup a, Semigroup b, Monoid a, Monoid b) => Monoid (Product a b) where
   mempty = Product mempty mempty
-  Product a1 b1 `mappend` Product a2 b2 = Product (a1 <> a2) (b1 <> b2)
+  mappend = (<>)
+
+instance (Semigroup a, Semigroup b) => Semigroup (Product a b) where
+  Product a1 b1 <> Product a2 b2 = Product (a1 <> a2) (b1 <> b2)
 
 instance Bifunctor Product where
   bimap fa fb (Product a b) = Product (fa a) (fb b)
diff --git a/src/Hpack/Config.hs b/src/Hpack/Config.hs
--- a/src/Hpack/Config.hs
+++ b/src/Hpack/Config.hs
@@ -80,7 +80,7 @@
 import qualified Data.HashMap.Lazy as HashMap
 import           Data.List (nub, (\\), sortBy, intercalate)
 import           Data.Maybe
-import           Data.Monoid hiding (Product)
+import           Data.Semigroup (Semigroup(..))
 import           Data.Ord
 import           Data.Text (Text)
 import qualified Data.Text as T
@@ -184,7 +184,10 @@
 
 instance Monoid LibrarySection where
   mempty = LibrarySection Nothing Nothing Nothing Nothing Nothing Nothing Nothing
-  mappend a b = LibrarySection {
+  mappend = (<>)
+
+instance Semigroup LibrarySection where
+  a <> b = LibrarySection {
       librarySectionExposed = librarySectionExposed b <|> librarySectionExposed a
     , librarySectionExposedModules = librarySectionExposedModules a <> librarySectionExposedModules b
     , librarySectionGeneratedExposedModules = librarySectionGeneratedExposedModules a <> librarySectionGeneratedExposedModules b
@@ -202,7 +205,10 @@
 
 instance Monoid ExecutableSection where
   mempty = ExecutableSection Nothing Nothing Nothing
-  mappend a b = ExecutableSection {
+  mappend = (<>)
+
+instance Semigroup ExecutableSection where
+  a <> b = ExecutableSection {
       executableSectionMain = executableSectionMain b <|> executableSectionMain a
     , executableSectionOtherModules = executableSectionOtherModules a <> executableSectionOtherModules b
     , executableSectionGeneratedOtherModules = executableSectionGeneratedOtherModules a <> executableSectionGeneratedOtherModules b
@@ -266,7 +272,7 @@
 type ParseCommonOptions = CommonOptions ParseCSources ParseCxxSources ParseJsSources
 instance FromValue a => FromValue (ParseCommonOptions a)
 
-instance (Monoid cSources, Monoid cxxSources, Monoid jsSources) => Monoid (CommonOptions cSources cxxSources jsSources a) where
+instance (Semigroup cSources, Semigroup cxxSources, Semigroup jsSources, Monoid cSources, Monoid cxxSources, Monoid jsSources) => Monoid (CommonOptions cSources cxxSources jsSources a) where
   mempty = CommonOptions {
     commonOptionsSourceDirs = Nothing
   , commonOptionsDependencies = Nothing
@@ -294,7 +300,10 @@
   , commonOptionsBuildTools = Nothing
   , commonOptionsVerbatim = Nothing
   }
-  mappend a b = CommonOptions {
+  mappend = (<>)
+
+instance (Semigroup cSources, Semigroup cxxSources, Semigroup jsSources) => Semigroup (CommonOptions cSources cxxSources jsSources a) where
+  a <> b = CommonOptions {
     commonOptionsSourceDirs = commonOptionsSourceDirs a <> commonOptionsSourceDirs b
   , commonOptionsDependencies = commonOptionsDependencies b <> commonOptionsDependencies a
   , commonOptionsPkgConfigDependencies = commonOptionsPkgConfigDependencies a <> commonOptionsPkgConfigDependencies b
@@ -428,8 +437,11 @@
 
 instance Monoid Empty where
   mempty = Empty
-  mappend Empty Empty = Empty
+  mappend = (<>)
 
+instance Semigroup Empty where
+  Empty <> Empty = Empty
+
 instance FromValue Empty where
   fromValue _ = return Empty
 
@@ -741,14 +753,14 @@
     }
 
 expandDefaults
-  :: (FromValue a, Monoid a)
+  :: (FromValue a, Semigroup a, Monoid a)
   => FilePath
   -> FilePath
   -> WithCommonOptionsWithDefaults a
   -> Warnings (Errors IO) (WithCommonOptions ParseCSources ParseCxxSources ParseJsSources a)
 expandDefaults userDataDir = expand []
   where
-    expand :: (FromValue a, Monoid a) =>
+    expand :: (FromValue a, Semigroup a, Monoid a) =>
          [FilePath]
       -> FilePath
       -> WithCommonOptionsWithDefaults a
@@ -757,7 +769,7 @@
       d <- mconcat <$> mapM (get seen dir) (fromMaybeList defaultsConfigDefaults)
       return (d <> c)
 
-    get :: forall a. (FromValue a, Monoid a) =>
+    get :: forall a. (FromValue a, Semigroup a, Monoid a) =>
          [FilePath]
       -> FilePath
       -> Defaults
diff --git a/src/Hpack/Syntax/Dependency.hs b/src/Hpack/Syntax/Dependency.hs
--- a/src/Hpack/Syntax/Dependency.hs
+++ b/src/Hpack/Syntax/Dependency.hs
@@ -13,6 +13,7 @@
 ) where
 
 import qualified Data.Text as T
+import           Data.Semigroup (Semigroup(..))
 import           Text.PrettyPrint (renderStyle, Style(..), Mode(..))
 import           Control.Monad
 import qualified Distribution.Compat.ReadP as D
@@ -32,7 +33,7 @@
 
 newtype Dependencies = Dependencies {
   unDependencies :: Map String DependencyVersion
-} deriving (Eq, Show, Monoid)
+} deriving (Eq, Show, Semigroup, Monoid)
 
 instance IsList Dependencies where
   type Item Dependencies = (String, DependencyVersion)