diff --git a/app/App/Commands.hs b/app/App/Commands.hs
--- a/app/App/Commands.hs
+++ b/app/App/Commands.hs
@@ -1,7 +1,6 @@
 module App.Commands where
 
 import App.Commands.CreateIndex
-import Data.Semigroup           ((<>))
 import Options.Applicative
 
 commands :: Parser (IO ())
diff --git a/app/App/Commands/CreateIndex.hs b/app/App/Commands/CreateIndex.hs
--- a/app/App/Commands/CreateIndex.hs
+++ b/app/App/Commands/CreateIndex.hs
@@ -9,7 +9,6 @@
 import Control.Lens
 import Control.Monad
 import Data.Generics.Product.Any
-import Data.Semigroup            ((<>))
 import Data.Word
 import Options.Applicative       hiding (columns)
 
diff --git a/app/Main.hs b/app/Main.hs
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -2,7 +2,6 @@
 
 import App.Commands
 import Control.Monad
-import Data.Semigroup      ((<>))
 import Options.Applicative
 
 main :: IO ()
diff --git a/bench/Main.hs b/bench/Main.hs
--- a/bench/Main.hs
+++ b/bench/Main.hs
@@ -5,7 +5,6 @@
 import Control.Monad
 import Criterion.Main
 import Data.List
-import Data.Monoid      ((<>))
 import Data.Word
 import System.Directory
 
diff --git a/doctest/DoctestDriver.hs b/doctest/DoctestDriver.hs
new file mode 100644
--- /dev/null
+++ b/doctest/DoctestDriver.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE CPP #-}
+
+#if MIN_VERSION_GLASGOW_HASKELL(8,4,4,0)
+{-# OPTIONS_GHC -F -pgmF doctest-discover #-}
+#else
+module Main where
+
+import qualified System.IO as IO
+
+main :: IO ()
+main = IO.putStrLn "WARNING: doctest will not run on GHC versions earlier than 8.4.4"
+#endif
diff --git a/hw-packed-vector.cabal b/hw-packed-vector.cabal
--- a/hw-packed-vector.cabal
+++ b/hw-packed-vector.cabal
@@ -1,119 +1,127 @@
-cabal-version:      2.2
+cabal-version: 2.2
 
-name:               hw-packed-vector
-version:            0.2.0.1
-synopsis:           Packed Vector
-description:        Packed Vector. Please see README.md
-category:           Data, Vector
-stability:          Experimental
-homepage:           http://github.com/haskell-works/hw-packed-vector#readme
-bug-reports:        https://github.com/haskell-works/hw-packed-vector/issues
-author:             John Ky
-maintainer:         newhoggy@gmail.com
-copyright:          2016-2019 John Ky
-license:            BSD-3-Clause
-license-file:       LICENSE
-tested-with:        GHC == 8.8.1, GHC == 8.6.5, GHC == 8.4.4, GHC == 8.2.2
-build-type:         Simple
-extra-source-files: README.md
+name:                   hw-packed-vector
+version:                0.2.1.0
+synopsis:               Packed Vector
+description:            Packed Vector. Please see README.md
+category:               Data, Vector
+stability:              Experimental
+homepage:               http://github.com/haskell-works/hw-packed-vector#readme
+bug-reports:            https://github.com/haskell-works/hw-packed-vector/issues
+author:                 John Ky
+maintainer:             newhoggy@gmail.com
+copyright:              2016-2020 John Ky
+license:                BSD-3-Clause
+license-file:           LICENSE
+tested-with:            GHC == 8.10.1, GHC == 8.8.3, GHC == 8.6.5, GHC == 8.4.4
+build-type:             Simple
+extra-source-files:     README.md
 
 source-repository head
   type: git
   location: https://github.com/haskell-works/hw-packed-vector
 
-common base                 { build-depends: base                 >= 4          && < 5      }
-
-common binary               { build-depends: binary               >= 0.8        && < 0.9    }
-common bytestring           { build-depends: bytestring           >= 0.10.8.2   && < 0.11   }
-common criterion            { build-depends: criterion            >= 1.4.1.0    && < 1.6    }
-common deepseq              { build-depends: deepseq              >= 1.4        && < 1.5    }
-common directory            { build-depends: directory            >= 1.3        && < 1.4    }
-common generic-lens         { build-depends: generic-lens         >= 1.1.0.0    && < 1.3    }
-common hedgehog             { build-depends: hedgehog             >= 0.6        && < 1.1    }
-common hspec                { build-depends: hspec                >= 2.7.1      && < 3      }
-common hw-bits              { build-depends: hw-bits              >= 0.7.0.6    && < 0.8    }
-common hw-hedgehog          { build-depends: hw-hedgehog          >= 0.1.0.3    && < 0.2    }
-common hw-hspec-hedgehog    { build-depends: hw-hspec-hedgehog    >= 0.1.0.7    && < 0.2    }
-common hw-prim              { build-depends: hw-prim              >= 0.6.2.27   && < 0.7    }
-common lens                 { build-depends: lens                 >= 4          && < 5      }
-common optparse-applicative { build-depends: optparse-applicative >= 0.14       && < 0.16   }
-common vector               { build-depends: vector               >= 0.12.0.3   && < 0.13   }
+common base                       { build-depends: base                       >= 4.11       && < 5      }
 
-common semigroups   { if impl(ghc <  8    ) { build-depends: semigroups     >= 0.16     && < 0.19 } }
+common binary                     { build-depends: binary                     >= 0.8        && < 0.9    }
+common bytestring                 { build-depends: bytestring                 >= 0.10.8.2   && < 0.11   }
+common doctest                    { build-depends: doctest                    >= 0.16.2     && < 0.17   }
+common doctest-discover           { build-depends: doctest-discover           >= 0.2        && < 0.3    }
+common criterion                  { build-depends: criterion                  >= 1.4.1.0    && < 1.6    }
+common deepseq                    { build-depends: deepseq                    >= 1.4        && < 1.5    }
+common directory                  { build-depends: directory                  >= 1.3        && < 1.4    }
+common generic-lens               { build-depends: generic-lens               >= 1.1.0.0    && < 1.3    }
+common hedgehog                   { build-depends: hedgehog                   >= 0.6        && < 1.1    }
+common hspec                      { build-depends: hspec                      >= 2.7.1      && < 3      }
+common hw-bits                    { build-depends: hw-bits                    >= 0.7.0.6    && < 0.8    }
+common hw-hedgehog                { build-depends: hw-hedgehog                >= 0.1.0.3    && < 0.2    }
+common hw-hspec-hedgehog          { build-depends: hw-hspec-hedgehog          >= 0.1.0.7    && < 0.2    }
+common hw-prim                    { build-depends: hw-prim                    >= 0.6.2.27   && < 0.7    }
+common lens                       { build-depends: lens                       >= 4          && < 5      }
+common optparse-applicative       { build-depends: optparse-applicative       >= 0.14       && < 0.16   }
+common vector                     { build-depends: vector                     >= 0.12.0.3   && < 0.13   }
 
 common config
   default-language:     Haskell2010
   ghc-options:          -Wall -O2 -msse4.2
 
+common hw-packed-vector
+  build-depends:        hw-packed-vector
+
 library
-  import:   base, config
-          , bytestring
-          , deepseq
-          , hw-bits
-          , hw-prim
-          , vector
-  exposed-modules:
-    HaskellWorks.Data.PackedVector
-    HaskellWorks.Data.PackedVector.Internal
-    HaskellWorks.Data.PackedVector.IO
-    HaskellWorks.Data.PackedVector.PackedVector64
-  other-modules:    Paths_hw_packed_vector
-  autogen-modules:  Paths_hw_packed_vector
-  hs-source-dirs:   src
+  import:               base, config
+                      , bytestring
+                      , deepseq
+                      , hw-bits
+                      , hw-prim
+                      , vector
+  exposed-modules:      HaskellWorks.Data.PackedVector
+                        HaskellWorks.Data.PackedVector.Internal
+                        HaskellWorks.Data.PackedVector.IO
+                        HaskellWorks.Data.PackedVector.PackedVector64
+  other-modules:        Paths_hw_packed_vector
+  autogen-modules:      Paths_hw_packed_vector
+  hs-source-dirs:       src
 
 executable hw-packed-vector
-  import:   base, config
-          , binary
-          , bytestring
-          , generic-lens
-          , hw-bits
-          , hw-prim
-          , lens
-          , optparse-applicative
-          , semigroups
-          , vector
+  import:               base, config
+                      , binary
+                      , bytestring
+                      , generic-lens
+                      , hw-bits
+                      , hw-prim
+                      , lens
+                      , optparse-applicative
+                      , vector
   main-is:              Main.hs
   hs-source-dirs:       app
   ghc-options:          -threaded -rtsopts -with-rtsopts=-N -O2
   build-depends:        hw-packed-vector
-  other-modules:
-      App.Commands
-      App.Commands.CreateIndex
-      App.Commands.Types
+  other-modules:        App.Commands
+                        App.Commands.CreateIndex
+                        App.Commands.Types
 
 test-suite hw-packed-vector-test
-  import:   base, config
-          , bytestring
-          , hedgehog
-          , hspec
-          , hw-bits
-          , hw-hedgehog
-          , hw-hspec-hedgehog
-          , hw-prim
-          , vector
+  import:               base, config
+                      , bytestring
+                      , hedgehog
+                      , hspec
+                      , hw-bits
+                      , hw-hedgehog
+                      , hw-hspec-hedgehog
+                      , hw-prim
+                      , vector
   type:                 exitcode-stdio-1.0
   main-is:              Spec.hs
-  other-modules:
-      HaskellWorks.Data.PackedVector.InternalSpec
-      HaskellWorks.Data.PackedVector.PackedVector64Spec
-      HaskellWorks.Gen
-      Paths_hw_packed_vector
+  other-modules:        HaskellWorks.Data.PackedVector.InternalSpec
+                        HaskellWorks.Data.PackedVector.PackedVector64Spec
+                        HaskellWorks.Gen
   hs-source-dirs:       test
   ghc-options:          -threaded -rtsopts -with-rtsopts=-N
   build-depends:        hw-packed-vector
   build-tool-depends:   hspec-discover:hspec-discover
 
 benchmark bench
-  import:   base, config
-          , criterion
-          , directory
-          , hedgehog
-          , hspec
-          , hw-prim
-          , vector
+  import:               base, config
+                      , criterion
+                      , directory
+                      , hedgehog
+                      , hspec
+                      , hw-prim
+                      , vector
   type:                 exitcode-stdio-1.0
   main-is:              Main.hs
   hs-source-dirs:       bench
-  other-modules:        Paths_hw_packed_vector
   build-depends:        hw-packed-vector
-  autogen-modules:      Paths_hw_packed_vector
+
+test-suite doctest
+  import:               base, config
+                      , doctest
+                      , doctest-discover
+                      , hw-packed-vector
+  default-language:     Haskell2010
+  type:                 exitcode-stdio-1.0
+  ghc-options:          -threaded
+  main-is:              DoctestDriver.hs
+  HS-Source-Dirs:       doctest
+  build-tool-depends:   doctest-discover:doctest-discover
diff --git a/src/HaskellWorks/Data/PackedVector/PackedVector64.hs b/src/HaskellWorks/Data/PackedVector/PackedVector64.hs
--- a/src/HaskellWorks/Data/PackedVector/PackedVector64.hs
+++ b/src/HaskellWorks/Data/PackedVector/PackedVector64.hs
@@ -12,7 +12,6 @@
 
 import Control.DeepSeq
 import Data.Int
-import Data.Semigroup                          ((<>))
 import Data.Word
 import GHC.Generics
 import HaskellWorks.Data.AtIndex
diff --git a/test/HaskellWorks/Data/PackedVector/InternalSpec.hs b/test/HaskellWorks/Data/PackedVector/InternalSpec.hs
--- a/test/HaskellWorks/Data/PackedVector/InternalSpec.hs
+++ b/test/HaskellWorks/Data/PackedVector/InternalSpec.hs
@@ -9,7 +9,7 @@
 import qualified Hedgehog.Gen     as G
 import qualified Hedgehog.Range   as R
 
-{-# ANN module ("HLint: Ignore Redundant do" :: String) #-}
+{-# ANN module ("HLint: ignore Redundant do" :: String) #-}
 
 spec :: Spec
 spec = describe "HaskellWorks.Data.PackedVector.InternalSpec" $ do
diff --git a/test/HaskellWorks/Data/PackedVector/PackedVector64Spec.hs b/test/HaskellWorks/Data/PackedVector/PackedVector64Spec.hs
--- a/test/HaskellWorks/Data/PackedVector/PackedVector64Spec.hs
+++ b/test/HaskellWorks/Data/PackedVector/PackedVector64Spec.hs
@@ -12,7 +12,7 @@
 import qualified Hedgehog.Gen                                  as G
 import qualified Hedgehog.Range                                as R
 
-{-# ANN module ("HLint: Ignore Redundant do" :: String) #-}
+{-# ANN module ("HLint: ignore Redundant do" :: String) #-}
 
 spec :: Spec
 spec = describe "HaskellWorks.Data.PackedVector.PackedVector64Spec" $ do
