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: 0.5.20180830
-#
-language: c
-dist: xenial
-git:
-  # whether to recursively clone submodules
-  submodules: false
-notifications:
-  irc:
-    channels:
-      - irc.freenode.org#haskell-lens
-    skip_join: true
-    template:
-      - "\"\\x0313trifecta\\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 $CABALHOME/packages/head.hackage
-matrix:
-  include:
-    - compiler: ghc-8.8.1
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.8.1","cabal-install-3.0"]}}
-    - compiler: ghc-8.6.5
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.6.5","cabal-install-3.0"]}}
-    - compiler: ghc-8.4.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.4.4","cabal-install-3.0"]}}
-    - compiler: ghc-8.2.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.2.2","cabal-install-3.0"]}}
-    - compiler: ghc-8.0.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.0.2","cabal-install-3.0"]}}
-    - compiler: ghc-7.10.3
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.10.3","cabal-install-3.0"]}}
-    - compiler: ghc-7.8.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.8.4","cabal-install-3.0"]}}
-    - compiler: ghc-head
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-head","cabal-install-head"]}}
-  allow_failures:
-    - compiler: ghc-head
-before_install:
-  - HC=$(echo "/opt/$CC/bin/ghc" | sed 's/-/\//')
-  - WITHCOMPILER="-w $HC"
-  - HADDOCK=$(echo "/opt/$CC/bin/haddock" | sed 's/-/\//')
-  - HCPKG="$HC-pkg"
-  - unset CC
-  - CABAL=/opt/ghc/bin/cabal
-  - CABALHOME=$HOME/.cabal
-  - export PATH="$CABALHOME/bin:$PATH"
-  - TOP=$(pwd)
-  - "HCNUMVER=$(${HC} --numeric-version|perl -ne '/^(\\d+)\\.(\\d+)\\.(\\d+)(\\.(\\d+))?$/; print(10000 * $1 + 100 * $2 + ($3 == 0 ? $5 != 1 : $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
-  - BENCH=--enable-benchmarks
-  - HEADHACKAGE=false
-  - if [ $HCNUMVER -gt 80801 ] ; then HEADHACKAGE=true ; fi
-  - rm -f $CABALHOME/config
-  - |
-    echo "verbose: normal +nowrap +markoutput"          >> $CABALHOME/config
-    echo "remote-build-reporting: anonymous"            >> $CABALHOME/config
-    echo "write-ghc-environment-files: always"          >> $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 $HEADHACKAGE; then
-    echo "allow-newer: $($HCPKG list --simple-output | sed -E 's/([a-zA-Z-]+)-[0-9.]+/*:\1/g')" >> $CABALHOME/config
-    echo "repository head.hackage.ghc.haskell.org"                                        >> $CABALHOME/config
-    echo "   url: https://ghc.gitlab.haskell.org/head.hackage/"                           >> $CABALHOME/config
-    echo "   secure: True"                                                                >> $CABALHOME/config
-    echo "   root-keys: 7541f32a4ccca4f97aea3b22f5e593ba2c0267546016b992dfadcd2fe944e55d" >> $CABALHOME/config
-    echo "              26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329" >> $CABALHOME/config
-    echo "              f76d08be13e9a61a377a85e2fb63f4c5435d40f8feb3e12eb05905edb8cdea89" >> $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 "packages: ./examples" >> cabal.project
-  - |
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(trifecta|trifecta-examples)$' || true) | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
-  - cat cabal.project || true
-  - cat cabal.project.local || true
-  - if [ -f "./configure.ac" ]; then (cd "." && autoreconf -i); fi
-  - if [ -f "./examples/configure.ac" ]; then (cd "./examples" && autoreconf -i); fi
-  - ${CABAL} v2-freeze $WITHCOMPILER ${TEST} ${BENCH} | color_cabal_output
-  - "cat cabal.project.freeze | sed -E 's/^(constraints: *| *)//' | sed 's/any.//'"
-  - rm  cabal.project.freeze
-  - ${CABAL} v2-build $WITHCOMPILER ${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 ${DISTDIR} || false
-  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec tar -xvf '{}' \;
-  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec rm       '{}' \;
-  - PKGDIR_trifecta="$(find . -maxdepth 1 -type d -regex '.*/trifecta-[0-9.]*')"
-  - PKGDIR_trifecta_examples="$(find . -maxdepth 1 -type d -regex '.*/trifecta-examples-[0-9.]*')"
-  # Generate cabal.project
-  - rm -rf cabal.project cabal.project.local cabal.project.freeze
-  - touch cabal.project
-  - |
-    echo "packages: ${PKGDIR_trifecta}" >> cabal.project
-    echo "packages: ${PKGDIR_trifecta_examples}" >> cabal.project
-  - |
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(trifecta|trifecta-examples)$' || true) | sed 's/^/constraints: /' | sed 's/$/ 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 $WITHCOMPILER ${TEST} ${BENCH} all | color_cabal_output
-  # Testing...
-  - ${CABAL} v2-test $WITHCOMPILER ${TEST} ${BENCH} all | color_cabal_output
-  # cabal check...
-  - (cd ${PKGDIR_trifecta} && ${CABAL} -vnormal check)
-  - (cd ${PKGDIR_trifecta_examples} && ${CABAL} -vnormal check)
-  # haddock...
-  - ${CABAL} v2-haddock $WITHCOMPILER --with-haddock $HADDOCK ${TEST} ${BENCH} all | color_cabal_output
-
-# 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 +1,9 @@
+2.1.1 [2021.02.18]
+------------------
+* 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.
+
 2.1 [2019.09.06]
 ----------------
 * Support building with `base-4.13` (GHC 8.8).
diff --git a/README.markdown b/README.markdown
--- a/README.markdown
+++ b/README.markdown
@@ -1,7 +1,7 @@
 trifecta
 ========
 
-[![Hackage](https://img.shields.io/hackage/v/trifecta.svg)](https://hackage.haskell.org/package/trifecta) [![Build Status](https://secure.travis-ci.org/ekmett/trifecta.png?branch=master)](http://travis-ci.org/ekmett/trifecta)
+[![Hackage](https://img.shields.io/hackage/v/trifecta.svg)](https://hackage.haskell.org/package/trifecta) [![Build Status](https://github.com/ekmett/trifecta/workflows/Haskell-CI/badge.svg)](https://github.com/ekmett/trifecta/actions?query=workflow%3AHaskell-CI)
 
 This package provides a parser that focuses on nice diagnostics.
 
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/Setup.lhs b/Setup.lhs
deleted file mode 100644
--- a/Setup.lhs
+++ /dev/null
@@ -1,34 +0,0 @@
-\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
-
-#endif
-
-\end{code}
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/examples/RFC2616-malformed.txt b/examples/RFC2616-malformed.txt
new file mode 100644
--- /dev/null
+++ b/examples/RFC2616-malformed.txt
@@ -0,0 +1,9 @@
+GET http://slashdot.org/ HTTP/1.1
+foo: this is a test
+
+GET http://slashdot.org/ HTTP/1.0
+foo: of the emergency broadcast system
+
+GET http://slashdot.org/ HTTP/1.0
+foo but I mangled the header
+
diff --git a/examples/trifecta-examples.cabal b/examples/trifecta-examples.cabal
--- a/examples/trifecta-examples.cabal
+++ b/examples/trifecta-examples.cabal
@@ -20,7 +20,8 @@
              , GHC == 8.2.2
              , GHC == 8.4.4
              , GHC == 8.6.5
-             , GHC == 8.8.1
+             , GHC == 8.8.4
+             , GHC == 8.10.3
 extra-source-files: RFC2616.txt RFC2616-malformed.txt
 
 source-repository head
diff --git a/src/Text/Trifecta/Rope.hs b/src/Text/Trifecta/Rope.hs
--- a/src/Text/Trifecta/Rope.hs
+++ b/src/Text/Trifecta/Rope.hs
@@ -50,8 +50,10 @@
 --
 -- >>> :set -XOverloadedStrings
 -- >>> import Data.Monoid ((<>))
+-- >>> import Data.ByteString (ByteString)
 -- >>> import qualified Data.ByteString.UTF8 as Strict
 -- >>> import qualified Data.ByteString.Lazy.UTF8 as Lazy
+-- >>> import Text.Trifecta.Delta
 
 -- A 'Strand' is a chunk of data; many 'Strand's together make a 'Rope'.
 data Strand
diff --git a/src/Text/Trifecta/Util/IntervalMap.hs b/src/Text/Trifecta/Util/IntervalMap.hs
--- a/src/Text/Trifecta/Util/IntervalMap.hs
+++ b/src/Text/Trifecta/Util/IntervalMap.hs
@@ -56,19 +56,22 @@
 import Control.Applicative hiding (empty)
 import Data.Foldable       (Foldable (foldMap))
 #endif
+import qualified Data.Foldable.WithIndex as WithIndex
 #if MIN_VERSION_lens(4,13,0) && __GLASGOW_HASKELL__ >= 710
-import Control.Lens hiding ((:<), (<|), (|>))
+import Control.Lens as Lens hiding ((:<), (<|), (|>))
 #else
-import Control.Lens hiding ((<|), (|>))
+import Control.Lens as Lens hiding ((<|), (|>))
 #endif
 import           Data.FingerTree
     (FingerTree, Measured (..), ViewL (..), (<|), (><))
 import qualified Data.FingerTree        as FT
+import qualified Data.Functor.WithIndex as WithIndex
 #if !(MIN_VERSION_base(4,11,0))
 import           Data.Semigroup
 #endif
 import           Data.Semigroup.Reducer
 import           Data.Semigroup.Union
+import qualified Data.Traversable.WithIndex as WithIndex
 
 ----------------------------------
 -- 4.8 Application: interval trees
@@ -111,20 +114,26 @@
 instance Functor (Node v) where
   fmap f (Node i x) = Node i (f x)
 
-instance FunctorWithIndex (Interval v) (Node v) where
+instance WithIndex.FunctorWithIndex (Interval v) (Node v) where
   imap f (Node i x) = Node i (f i x)
 
 instance Foldable (Node v) where
   foldMap f (Node _ x) = f x
 
-instance FoldableWithIndex (Interval v) (Node v) where
+instance WithIndex.FoldableWithIndex (Interval v) (Node v) where
   ifoldMap f (Node k v) = f k v
 
 instance Traversable (Node v) where
   traverse f (Node i x) = Node i <$> f x
 
-instance TraversableWithIndex (Interval v) (Node v) where
+instance WithIndex.TraversableWithIndex (Interval v) (Node v) where
   itraverse f (Node i x) = Node i <$> f i x
+
+#if !MIN_VERSION_lens(5,0,0)
+instance Lens.FunctorWithIndex     (Interval v) (Node v) where imap      = WithIndex.imap
+instance Lens.FoldableWithIndex    (Interval v) (Node v) where ifoldMap  = WithIndex.ifoldMap
+instance Lens.TraversableWithIndex (Interval v) (Node v) where itraverse = WithIndex.itraverse
+#endif
 
 -- rightmost interval (including largest lower bound) and largest upper bound.
 data IntInterval v = NoInterval | IntInterval (Interval v) v
diff --git a/src/Text/Trifecta/Util/It.hs b/src/Text/Trifecta/Util/It.hs
--- a/src/Text/Trifecta/Util/It.hs
+++ b/src/Text/Trifecta/Util/It.hs
@@ -49,6 +49,7 @@
 -- >>> import Control.Comonad (extract)
 -- >>> import Data.ByteString as Strict
 -- >>> import Text.Trifecta.Delta
+-- >>> import Text.Trifecta.Rope
 -- >>> import Text.Trifecta.Util.It
 
 -- | @'It'@ is an <https://wiki.haskell.org/Enumerator_and_iteratee Iteratee>
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/trifecta.cabal b/trifecta.cabal
--- a/trifecta.cabal
+++ b/trifecta.cabal
@@ -1,6 +1,6 @@
 name:          trifecta
 category:      Text, Parsing, Diagnostics, Pretty Printer, Logging
-version:       2.1
+version:       2.1.1
 license:       BSD3
 cabal-version: 1.18
 license-file:  LICENSE
@@ -20,14 +20,15 @@
   .
   <images/example.png (Local Copy)>
 
-build-type:    Custom
+build-type:    Simple
 tested-with:   GHC == 7.8.4
              , GHC == 7.10.3
              , GHC == 8.0.2
              , GHC == 8.2.2
              , GHC == 8.4.4
              , GHC == 8.6.5
-             , GHC == 8.8.1
+             , GHC == 8.8.4
+             , GHC == 8.10.3
 
 extra-doc-files:
   images/*.png
@@ -37,22 +38,15 @@
   examples/LICENSE
   examples/rfc2616/*.hs
   examples/RFC2616.txt
+  examples/RFC2616-malformed.txt
   examples/trifecta-examples.cabal
-  .travis.yml
   CHANGELOG.markdown
   README.markdown
-  Warning.hs
 
 source-repository head
   type: git
   location: https://github.com/ekmett/trifecta
 
-custom-setup
-  setup-depends:
-    base          >= 4 && < 5,
-    Cabal,
-    cabal-doctest >= 1 && < 1.1
-
 library
   exposed-modules:
     Text.Trifecta
@@ -72,13 +66,13 @@
     Text.Trifecta.Util.Pretty
 
   build-depends:
-    ansi-terminal               >= 0.6     && < 0.11,
+    ansi-terminal               >= 0.6     && < 0.12,
     array                       >= 0.3.0.2 && < 0.6,
     base                        >= 4.7     && < 5,
     blaze-builder               >= 0.3.0.1 && < 0.5,
     blaze-html                  >= 0.5     && < 0.10,
     blaze-markup                >= 0.5     && < 0.9,
-    bytestring                  >= 0.9.1   && < 0.11,
+    bytestring                  >= 0.9.1   && < 0.12,
     charset                     >= 0.3.5.1 && < 1,
     comonad                     >= 4       && < 6,
     containers                  >= 0.3     && < 0.7,
@@ -86,14 +80,14 @@
     fingertree                  >= 0.1     && < 0.2,
     ghc-prim,
     hashable                    >= 1.2.1   && < 1.4,
-    lens                        >= 4.0     && < 5,
+    indexed-traversable         >= 0.1.1   && < 0.2,
+    lens                        >= 4.0     && < 6,
     mtl                         >= 2.0.1   && < 2.3,
     parsers                     >= 0.12.1  && < 1,
     prettyprinter               >= 1.2     && < 2,
     prettyprinter-ansi-terminal >= 1.1     && < 2,
     profunctors                 >= 4.0     && < 6,
     reducers                    >= 3.10    && < 4,
-    semigroups                  >= 0.8.3.1 && < 1,
     transformers                >= 0.2     && < 0.6,
     unordered-containers        >= 0.2.1   && < 0.3,
     utf8-string                 >= 0.3.6   && < 1.1
@@ -108,19 +102,9 @@
     if !impl(ghc >= 8.8)
       ghc-options: -Wnoncanonical-monadfail-instances
   else
-    build-depends: fail == 4.9.*
-
-test-suite doctests
-  type:              exitcode-stdio-1.0
-  main-is:           doctests.hs
-  ghc-options:       -Wall -threaded
-  x-doctest-options: -fobject-code
-  hs-source-dirs:    tests
-  default-language:  Haskell2010
-  build-depends:
-    base,
-    doctest >= 0.11.1 && < 0.17,
-    trifecta
+    build-depends:
+      fail                      == 4.9.*,
+      semigroups                >= 0.8.3.1 && < 1
 
 test-suite quickcheck
   type:    exitcode-stdio-1.0
