diff --git a/.hlint.yaml b/.hlint.yaml
new file mode 100644
--- /dev/null
+++ b/.hlint.yaml
@@ -0,0 +1,4 @@
+- arguments: [--cpp-ansi]
+
+- ignore: {name: Use import/export shortcut}
+- ignore: {name: Use fmap}
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
--- a/.travis.yml
+++ /dev/null
@@ -1,173 +0,0 @@
-# This Travis job script has been generated by a script via
-#
-#   haskell-ci '--output=.travis.yml' '--config=cabal.haskell-ci' 'cabal.project'
-#
-# For more information, see https://github.com/haskell-CI/haskell-ci
-#
-# version: 0.3.20190425
-#
-language: c
-dist: xenial
-git:
-  # whether to recursively clone submodules
-  submodules: false
-notifications:
-  irc:
-    channels:
-      - irc.freenode.org#haskell-lens
-    skip_join: true
-    template:
-      - "\"\\x0313approximate\\x03/\\x0306%{branch}\\x03 \\x0314%{commit}\\x03 %{build_url} %{message}\""
-cache:
-  directories:
-    - $HOME/.cabal/packages
-    - $HOME/.cabal/store
-before_cache:
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/build-reports.log
-  # remove files that are regenerated by 'cabal update'
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/00-index.*
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/*.json
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.cache
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.tar
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.tar.idx
-  - rm -rfv $CABALHOME/packages/head.hackage
-matrix:
-  include:
-    - compiler: ghc-8.8.1
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.8.1","cabal-install-3.0"]}}
-      env: GHCHEAD=true
-    - compiler: ghc-8.6.5
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.6.5","cabal-install-2.4"]}}
-    - compiler: ghc-8.4.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.4.4","cabal-install-2.4"]}}
-    - compiler: ghc-8.2.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.2.2","cabal-install-2.4"]}}
-    - compiler: ghc-8.0.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.0.2","cabal-install-2.4"]}}
-    - compiler: ghc-7.10.3
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.10.3","cabal-install-2.4"]}}
-    - compiler: ghc-7.8.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.8.4","cabal-install-2.4"]}}
-    - compiler: ghc-7.6.3
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.6.3","cabal-install-2.4"]}}
-    - compiler: ghc-7.4.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.4.2","cabal-install-2.4"]}}
-    - compiler: ghc-head
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-head","cabal-install-head"]}}
-      env: GHCHEAD=true
-  allow_failures:
-    - compiler: ghc-head
-    - compiler: ghc-8.8.1
-before_install:
-  - HC=$(echo "/opt/$CC/bin/ghc" | sed 's/-/\//')
-  - HCPKG="$HC-pkg"
-  - unset CC
-  - CABAL=/opt/ghc/bin/cabal
-  - CABALHOME=$HOME/.cabal
-  - export PATH="$CABALHOME/bin:$PATH"
-  - TOP=$(pwd)
-  - HCNUMVER=$(( $(${HC} --numeric-version|sed -E 's/([0-9]+)\.([0-9]+)\.([0-9]+).*/\1 * 10000 + \2 * 100 + \3/') ))
-  - echo $HCNUMVER
-  - CABAL="$CABAL -vnormal+nowrap+markoutput"
-  - set -o pipefail
-  - |
-    echo 'function blue(s) { printf "\033[0;34m" s "\033[0m " }'           >> .colorful.awk
-    echo 'BEGIN { state = "output"; }'                                     >> .colorful.awk
-    echo '/^-----BEGIN CABAL OUTPUT-----$/ { state = "cabal" }'            >> .colorful.awk
-    echo '/^-----END CABAL OUTPUT-----$/ { state = "output" }'             >> .colorful.awk
-    echo '!/^(-----BEGIN CABAL OUTPUT-----|-----END CABAL OUTPUT-----)/ {' >> .colorful.awk
-    echo '  if (state == "cabal") {'                                       >> .colorful.awk
-    echo '    print blue($0)'                                              >> .colorful.awk
-    echo '  } else {'                                                      >> .colorful.awk
-    echo '    print $0'                                                    >> .colorful.awk
-    echo '  }'                                                             >> .colorful.awk
-    echo '}'                                                               >> .colorful.awk
-  - cat .colorful.awk
-  - |
-    color_cabal_output () {
-      awk -f $TOP/.colorful.awk
-    }
-  - echo text | color_cabal_output
-install:
-  - ${CABAL} --version
-  - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
-  - TEST=--enable-tests
-  - if [ $HCNUMVER -lt 70800 ] ; then TEST=--disable-tests ; fi
-  - BENCH=--enable-benchmarks
-  - GHCHEAD=${GHCHEAD-false}
-  - rm -f $CABALHOME/config
-  - |
-    echo "verbose: normal +nowrap +markoutput"          >> $CABALHOME/config
-    echo "remote-build-reporting: anonymous"            >> $CABALHOME/config
-    echo "remote-repo-cache: $CABALHOME/packages"       >> $CABALHOME/config
-    echo "logs-dir:          $CABALHOME/logs"           >> $CABALHOME/config
-    echo "world-file:        $CABALHOME/world"          >> $CABALHOME/config
-    echo "extra-prog-path:   $CABALHOME/bin"            >> $CABALHOME/config
-    echo "symlink-bindir:    $CABALHOME/bin"            >> $CABALHOME/config
-    echo "installdir:        $CABALHOME/bin"            >> $CABALHOME/config
-    echo "build-summary:     $CABALHOME/logs/build.log" >> $CABALHOME/config
-    echo "store-dir:         $CABALHOME/store"          >> $CABALHOME/config
-    echo "install-dirs user"                            >> $CABALHOME/config
-    echo "  prefix: $CABALHOME"                         >> $CABALHOME/config
-    echo "repository hackage.haskell.org"               >> $CABALHOME/config
-    echo "  url: http://hackage.haskell.org/"           >> $CABALHOME/config
-  - |
-    if $GHCHEAD; then
-    echo "allow-newer: $($HCPKG list --simple-output | sed -E 's/([a-zA-Z-]+)-[0-9.]+/*:\1/g')" >> $CABALHOME/config
-    
-    echo "repository head.hackage"                                                        >> $CABALHOME/config
-    echo "   url: http://head.hackage.haskell.org/"                                       >> $CABALHOME/config
-    echo "   secure: True"                                                                >> $CABALHOME/config
-    echo "   root-keys: 07c59cb65787dedfaef5bd5f987ceb5f7e5ebf88b904bbd4c5cbdeb2ff71b740" >> $CABALHOME/config
-    echo "              2e8555dde16ebd8df076f1a8ef13b8f14c66bad8eafefd7d9e37d0ed711821fb" >> $CABALHOME/config
-    echo "              8f79fd2389ab2967354407ec852cbe73f2e8635793ac446d09461ffb99527f6e" >> $CABALHOME/config
-    echo "   key-threshold: 3"                                                            >> $CABALHOME/config
-    fi
-  - cat $CABALHOME/config
-  - rm -fv cabal.project cabal.project.local cabal.project.freeze
-  - travis_retry ${CABAL} v2-update -v
-  # Generate cabal.project
-  - rm -rf cabal.project cabal.project.local cabal.project.freeze
-  - touch cabal.project
-  - |
-    echo 'packages: "."' >> cabal.project
-  - |
-    echo "write-ghc-environment-files: always" >> cabal.project
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | grep -vE -- '^(approximate)$' | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
-  - cat cabal.project || true
-  - cat cabal.project.local || true
-  - if [ -f "./configure.ac" ]; then (cd "." && autoreconf -i); fi
-  - ${CABAL} v2-freeze -w ${HC} ${TEST} ${BENCH} | color_cabal_output
-  - "cat cabal.project.freeze | sed -E 's/^(constraints: *| *)//' | sed 's/any.//'"
-  - rm  cabal.project.freeze
-  - ${CABAL} v2-build -w ${HC} ${TEST} ${BENCH} --dep -j2 all | color_cabal_output
-script:
-  - DISTDIR=$(mktemp -d /tmp/dist-test.XXXX)
-  # Packaging...
-  - ${CABAL} v2-sdist all | color_cabal_output
-  # Unpacking...
-  - mv dist-newstyle/sdist/*.tar.gz ${DISTDIR}/
-  - cd ${DISTDIR} || false
-  - find . -maxdepth 1 -name '*.tar.gz' -exec tar -xvf '{}' \;
-  # Generate cabal.project
-  - rm -rf cabal.project cabal.project.local cabal.project.freeze
-  - touch cabal.project
-  - |
-    echo 'packages: "approximate-*/*.cabal"' >> cabal.project
-  - |
-    echo "write-ghc-environment-files: always" >> cabal.project
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | grep -vE -- '^(approximate)$' | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
-  - cat cabal.project || true
-  - cat cabal.project.local || true
-  # Building with tests and benchmarks...
-  # build & run tests, build benchmarks
-  - ${CABAL} v2-build -w ${HC} ${TEST} ${BENCH} all | color_cabal_output
-  # Testing...
-  - if [ $HCNUMVER -ge 70800 ] ; then ${CABAL} v2-test -w ${HC} ${TEST} ${BENCH} all | color_cabal_output ; fi
-  # cabal check...
-  - (cd approximate-* && ${CABAL} -vnormal check)
-  # haddock...
-  - if [ $HCNUMVER -lt 80200 ]  ||  [ $HCNUMVER -ge 80400 ] ; then ${CABAL} v2-haddock -w ${HC} ${TEST} ${BENCH} all | color_cabal_output ; fi
-
-# REGENDATA ["--output=.travis.yml","--config=cabal.haskell-ci","cabal.project"]
-# EOF
diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,11 @@
+0.3.3 [2021.02.17]
+------------------
+* Allow building with `lens-5.*`.
+* The build-type has been changed from `Custom` to `Simple`.
+  To achieve this, the `doctests` test suite has been removed in favor of using
+  [`cabal-docspec`](https://github.com/phadej/cabal-extras/tree/master/cabal-docspec)
+  to run the doctests.
+
 0.3.2 [2019.09.13]
 ------------------
 * Allow building with `safecopy-0.10`.
diff --git a/HLint.hs b/HLint.hs
deleted file mode 100644
--- a/HLint.hs
+++ /dev/null
@@ -1,1 +0,0 @@
-ignore "Use import/export shortcut"
diff --git a/README.markdown b/README.markdown
--- a/README.markdown
+++ b/README.markdown
@@ -1,7 +1,7 @@
 approximate
 ===========
 
-[![Hackage](https://img.shields.io/hackage/v/approximate.svg)](https://hackage.haskell.org/package/approximate) [![Build Status](https://secure.travis-ci.org/ekmett/approximate.png?branch=master)](http://travis-ci.org/ekmett/approximate)
+[![Hackage](https://img.shields.io/hackage/v/approximate.svg)](https://hackage.haskell.org/package/approximate) [![Build Status](https://github.com/ekmett/approximate/workflows/Haskell-CI/badge.svg)](https://github.com/ekmett/approximate/actions?query=workflow%3AHaskell-CI)
 
 This package provides approximate numbers and discrete values with lower bounds on their probability of correctness.
 
diff --git a/Setup.lhs b/Setup.lhs
--- a/Setup.lhs
+++ b/Setup.lhs
@@ -1,34 +1,7 @@
-\begin{code}
-{-# LANGUAGE CPP #-}
-{-# OPTIONS_GHC -Wall #-}
-module Main (main) where
-
-#ifndef MIN_VERSION_cabal_doctest
-#define MIN_VERSION_cabal_doctest(x,y,z) 0
-#endif
-
-#if MIN_VERSION_cabal_doctest(1,0,0)
-
-import Distribution.Extra.Doctest ( defaultMainWithDoctests )
-main :: IO ()
-main = defaultMainWithDoctests "doctests"
-
-#else
-
-#ifdef MIN_VERSION_Cabal
--- If the macro is defined, we have new cabal-install,
--- but for some reason we don't have cabal-doctest in package-db
---
--- Probably we are running cabal sdist, when otherwise using new-build
--- workflow
-import Warning ()
-#endif
-
-import Distribution.Simple
-
-main :: IO ()
-main = defaultMain
+#!/usr/bin/runhaskell
+> module Main (main) where
 
-#endif
+> import Distribution.Simple
 
-\end{code}
+> main :: IO ()
+> main = defaultMain
diff --git a/Warning.hs b/Warning.hs
deleted file mode 100644
--- a/Warning.hs
+++ /dev/null
@@ -1,5 +0,0 @@
-module Warning
-  {-# WARNING ["You are configuring this package without cabal-doctest installed.",
-               "The doctests test-suite will not work as a result.",
-               "To fix this, install cabal-doctest before configuring."] #-}
-  () where
diff --git a/approximate.cabal b/approximate.cabal
--- a/approximate.cabal
+++ b/approximate.cabal
@@ -1,8 +1,8 @@
 name:          approximate
 category:      Numeric
-version:       0.3.2
+version:       0.3.3
 license:       BSD3
-cabal-version: >= 1.8
+cabal-version: >= 1.10
 license-file:  LICENSE
 author:        Edward A. Kmett
 maintainer:    Edward A. Kmett <ekmett@gmail.com>
@@ -10,7 +10,7 @@
 homepage:      http://github.com/analytics/approximate/
 bug-reports:   http://github.com/analytics/approximate/issues
 copyright:     Copyright (C) 2013 Edward A. Kmett
-build-type:    Custom
+build-type:    Simple
 tested-with:   GHC == 7.4.2
              , GHC == 7.6.3
              , GHC == 7.8.4
@@ -19,38 +19,24 @@
              , GHC == 8.2.2
              , GHC == 8.4.4
              , GHC == 8.6.5
-             , GHC == 8.8.1
+             , GHC == 8.8.3
+             , GHC == 8.10.1
 synopsis:      Approximate discrete values and numbers
 description:   This package provides approximate discrete values and numbers.
 
 extra-source-files:
-  .travis.yml
   .ghci
   .gitignore
+  .hlint.yaml
   .vim.custom
-  travis/cabal-apt-install
-  travis/config
   AUTHORS.markdown
   README.markdown
   CHANGELOG.markdown
-  HLint.hs
-  Warning.hs
 
-custom-setup
-  setup-depends:
-    base          >= 4.3 && <5,
-    Cabal         >= 1.10,
-    cabal-doctest >= 1 && <1.1
-
 source-repository head
   type: git
   location: git://github.com/analytics/approximate.git
 
--- You can disable the doctests test suite with -f-test-doctests
-flag test-doctests
-  default: True
-  manual: True
-
 flag herbie
   default: False
   manual: True
@@ -65,7 +51,7 @@
     deepseq                   >= 1.3      && < 1.5,
     ghc-prim,
     hashable                  >= 1.2.5    && < 1.4,
-    lens                      >= 3.9      && < 5,
+    lens                      >= 3.9      && < 6,
     log-domain,
     pointed                   >= 3        && < 6,
     semigroupoids             >= 3.0.2    && < 6,
@@ -90,21 +76,4 @@
   c-sources: cbits/fast.c
   ghc-options: -Wall -fwarn-tabs -O2
   hs-source-dirs: src
-
-test-suite doctests
-  type:           exitcode-stdio-1.0
-  main-is:        doctests.hs
-  ghc-options:    -Wall -threaded
-  hs-source-dirs: tests
-
-  if !flag(test-doctests)
-    buildable: False
-  else
-    build-depends:
-      approximate,
-      base,
-      directory      >= 1.0,
-      doctest        >= 0.9.1,
-      filepath,
-      semigroups     >= 0.9,
-      simple-reflect >= 0.3.1
+  default-language: Haskell2010
diff --git a/src/Data/Approximate/Mass.hs b/src/Data/Approximate/Mass.hs
--- a/src/Data/Approximate/Mass.hs
+++ b/src/Data/Approximate/Mass.hs
@@ -49,6 +49,9 @@
 import GHC.Generics
 import Numeric.Log
 
+-- $setup
+-- >>> import Control.Monad (replicateM)
+
 -- | A quantity with a lower-bound on its probability mass. This represents
 -- a 'probable value' as a 'Monad' that you can use to calculate progressively
 -- less likely consequences.
@@ -65,6 +68,11 @@
 -- Also note that @('&?')@ and @('|?')@ are able to use knowledge about the
 -- function to get better precision on their results than naively using
 -- @'liftA2' ('&&')@
+--
+-- >>> let z = Mass 0.875 'z'
+-- >>> replicateM 3 z
+-- Mass 0.669921875 "zzz"
+--
 data Mass a = Mass {-# UNPACK #-} !(Log Double) a
   deriving (Eq,Ord,Show,Read,Typeable,Data,Generic)
 
diff --git a/src/Data/Approximate/Type.hs b/src/Data/Approximate/Type.hs
--- a/src/Data/Approximate/Type.hs
+++ b/src/Data/Approximate/Type.hs
@@ -1,5 +1,4 @@
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE TemplateHaskell #-}
@@ -144,7 +143,7 @@
   {-# INLINE elemseq #-}
 
 instance NFData a => NFData (Approximate a) where
-  rnf (Approximate _ l m h) = rnf l `seq` rnf m `seq` rnf h `seq` ()
+  rnf (Approximate _ l m h) = rnf l `seq` rnf m `seq` rnf h
 
 instance Functor Approximate where
   fmap f (Approximate p l m h) = Approximate p (f l) (f m) (f h)
diff --git a/tests/doctests.hs b/tests/doctests.hs
deleted file mode 100644
--- a/tests/doctests.hs
+++ /dev/null
@@ -1,25 +0,0 @@
------------------------------------------------------------------------------
--- |
--- Module      :  Main (doctests)
--- Copyright   :  (C) 2012-14 Edward Kmett
--- License     :  BSD-style (see the file LICENSE)
--- Maintainer  :  Edward Kmett <ekmett@gmail.com>
--- Stability   :  provisional
--- Portability :  portable
---
--- This module provides doctests for a project based on the actual versions
--- of the packages it was built with. It requires a corresponding Setup.lhs
--- to be added to the project
------------------------------------------------------------------------------
-module Main where
-
-import Build_doctests (flags, pkgs, module_sources)
-import Data.Foldable (traverse_)
-import Test.DocTest
-
-main :: IO ()
-main = do
-    traverse_ putStrLn args
-    doctest args
-  where
-    args = flags ++ pkgs ++ module_sources
diff --git a/travis/cabal-apt-install b/travis/cabal-apt-install
deleted file mode 100644
--- a/travis/cabal-apt-install
+++ /dev/null
@@ -1,27 +0,0 @@
-#! /bin/bash
-set -eu
-
-APT="sudo apt-get -q -y"
-CABAL_INSTALL_DEPS="cabal install --only-dependencies --force-reinstall"
-
-$APT update
-$APT install dctrl-tools
-
-# Find potential system packages to satisfy cabal dependencies
-deps()
-{
-	local M='^\([^ ]\+\)-[0-9.]\+ (.*$'
-	local G=' -o ( -FPackage -X libghc-\L\1\E-dev )'
-	local E="$($CABAL_INSTALL_DEPS "$@" --dry-run -v 2> /dev/null \
-		| sed -ne "s/$M/$G/p" | sort -u)"
-	grep-aptavail -n -sPackage \( -FNone -X None \) $E | sort -u
-}
-
-$APT install $(deps "$@") libghc-quickcheck2-dev # QuickCheck is special
-$CABAL_INSTALL_DEPS "$@" # Install the rest via Hackage
-
-if ! $APT install hlint ; then
-	$APT install $(deps hlint)
-	cabal install hlint
-fi
-
diff --git a/travis/config b/travis/config
deleted file mode 100644
--- a/travis/config
+++ /dev/null
@@ -1,16 +0,0 @@
--- This provides a custom ~/.cabal/config file for use when hackage is down that should work on unix
---
--- This is particularly useful for travis-ci to get it to stop complaining
--- about a broken build when everything is still correct on our end.
---
--- This uses Luite Stegeman's mirror of hackage provided by his 'hdiff' site instead
---
--- To enable this, uncomment the before_script in .travis.yml
-
-remote-repo: hdiff.luite.com:http://hdiff.luite.com/packages/archive
-remote-repo-cache: ~/.cabal/packages
-world-file: ~/.cabal/world
-build-summary: ~/.cabal/logs/build.log
-remote-build-reporting: anonymous
-install-dirs user
-install-dirs global