diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
--- a/.travis.yml
+++ /dev/null
@@ -1,178 +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:
-      - "\"\\x0313either\\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 $CABALHOME/packages/head.hackage
-matrix:
-  include:
-    - compiler: ghc-8.8.1
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.8.1","cabal-install-3.0"]}}
-      env: GHCHEAD=true
-    - compiler: ghc-8.6.5
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.6.5","cabal-install-2.4"]}}
-    - compiler: ghc-8.4.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.4.4","cabal-install-2.4"]}}
-    - compiler: ghc-8.2.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.2.2","cabal-install-2.4"]}}
-    - compiler: ghc-8.0.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.0.2","cabal-install-2.4"]}}
-    - compiler: ghc-7.10.3
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.10.3","cabal-install-2.4"]}}
-    - compiler: ghc-7.8.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.8.4","cabal-install-2.4"]}}
-    - compiler: ghc-7.6.3
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.6.3","cabal-install-2.4"]}}
-    - compiler: ghc-7.4.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.4.2","cabal-install-2.4"]}}
-    - compiler: ghc-7.2.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.2.2","cabal-install-2.4"]}}
-    - compiler: ghc-7.0.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.0.4","cabal-install-2.4"]}}
-    - compiler: ghc-head
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-head","cabal-install-head"]}}
-      env: GHCHEAD=true
-  allow_failures:
-    - compiler: ghc-head
-    - compiler: ghc-7.0.4
-    - compiler: ghc-7.2.2
-    - compiler: ghc-8.8.1
-before_install:
-  - HC=$(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:
-  - ${CABAL} --version
-  - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
-  - TEST=--enable-tests
-  - BENCH=--enable-benchmarks
-  - GHCHEAD=${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 -- '^(either)$' | sed 's/^/constraints: /' | sed 's/$/ 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: "either-*/*.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 -- '^(either)$' | sed 's/^/constraints: /' | sed 's/$/ 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...
-  - ${CABAL} v2-test -w ${HC} ${TEST} ${BENCH} all | color_cabal_output
-  # cabal check...
-  - (cd either-* && ${CABAL} -vnormal check)
-  # haddock...
-  - ${CABAL} v2-haddock -w ${HC} ${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 +1,8 @@
+5.0.2 [2022.05.07]
+------------------
+* Tweak error messages of `fromRight'` and `fromLeft'` for clarity.
+* Allow building with `mtl-2.3.*`.
+
 5.0.1.1 [2019.05.02]
 --------------------
 * Only incur a `semigroups` dependency on pre-8.0 GHCs.
diff --git a/README.markdown b/README.markdown
--- a/README.markdown
+++ b/README.markdown
@@ -1,7 +1,7 @@
 either
 ======
 
-[![Hackage](https://img.shields.io/hackage/v/either.svg)](https://hackage.haskell.org/package/either) [![Build Status](https://secure.travis-ci.org/ekmett/either.png?branch=master)](http://travis-ci.org/ekmett/either)
+[![Hackage](https://img.shields.io/hackage/v/either.svg)](https://hackage.haskell.org/package/either) [![Build Status](https://github.com/ekmett/either/workflows/Haskell-CI/badge.svg)](https://github.com/ekmett/either/actions?query=workflow%3AHaskell-CI)
 
 Contact Information
 -------------------
diff --git a/either.cabal b/either.cabal
--- a/either.cabal
+++ b/either.cabal
@@ -1,6 +1,6 @@
 name:          either
 category:      Control, Monads
-version:       5.0.1.1
+version:       5.0.2
 license:       BSD3
 cabal-version: >= 1.10
 license-file:  LICENSE
@@ -23,12 +23,13 @@
              , GHC == 8.2.2
              , GHC == 8.4.4
              , GHC == 8.6.5
-             , GHC == 8.8.1
+             , GHC == 8.8.4
+             , GHC == 8.10.4
+             , GHC == 9.0.1
 extra-source-files:
   .gitignore
   .ghci
   .vim.custom
-  .travis.yml
   CHANGELOG.markdown
   README.markdown
 
@@ -40,7 +41,7 @@
   build-depends:
     base              >= 4       && < 5,
     bifunctors        >= 4       && < 6,
-    mtl               >= 2.0     && < 2.3,
+    mtl               >= 2.0     && < 2.4,
     profunctors       >= 4       && < 6,
     semigroupoids     >= 4       && < 6
 
@@ -65,5 +66,5 @@
     either,
     test-framework             >= 0.8.1.1 && < 0.9,
     test-framework-quickcheck2 >= 0.3.0.3 && < 0.4,
-    QuickCheck                 >= 2.9     && < 2.14
+    QuickCheck                 >= 2.9     && < 2.15
   default-language: Haskell2010
diff --git a/src/Data/Either/Combinators.hs b/src/Data/Either/Combinators.hs
--- a/src/Data/Either/Combinators.hs
+++ b/src/Data/Either/Combinators.hs
@@ -93,7 +93,7 @@
 -- >>> fromLeft' (Left 12)
 -- 12
 fromLeft' :: Either a b -> a
-fromLeft' (Right _) = error "Data.Either.Combinators.fromLeft: Argument takes form 'Right _'" -- yuck
+fromLeft' (Right _) = error "Data.Either.Combinators.fromLeft' encountered a value of form 'Right _', consider using Data.Either.Combinators.fromLeft with a default value." -- yuck
 fromLeft' (Left x)  = x
 
 -- | Extracts the element out of a 'Right' and
@@ -108,7 +108,7 @@
 -- >>> fromRight' (Right 12)
 -- 12
 fromRight' :: Either a b -> b
-fromRight' (Left _)  = error "Data.Either.Combinators.fromRight: Argument takes form 'Left _'" -- yuck
+fromRight' (Left _)  = error "Data.Either.Combinators.fromRight' encountered a value of form 'Left _', consider using Data.Either.Combinators.fromRight with a default value." -- yuck
 fromRight' (Right x) = x
 
 -- | The 'mapBoth' function takes two functions and applies the first if iff the value
@@ -313,10 +313,10 @@
 
 -- | Maybe produce a 'Left', otherwise produce a 'Right'.
 --
--- >>> maybeToRight "default" (Just 12)
+-- >>> maybeToLeft "default" (Just 12)
 -- Left 12
 --
--- >>> maybeToRight "default" Nothing
+-- >>> maybeToLeft "default" Nothing
 -- Right "default"
 maybeToLeft :: b -> Maybe a -> Either a b
 maybeToLeft _ (Just x) = Left x
@@ -342,13 +342,11 @@
 
 -- | Swap the 'Left' and 'Right' sides of an 'Either'.
 --
--- @
 -- >>> swapEither (Right 3)
 -- Left 3
 --
 -- >>> swapEither (Left "error")
 -- Right "error"
--- @
 swapEither :: Either e a -> Either a e
 swapEither = either Right Left
 {-# INLINE swapEither #-}
diff --git a/src/Data/Either/Validation.hs b/src/Data/Either/Validation.hs
--- a/src/Data/Either/Validation.hs
+++ b/src/Data/Either/Validation.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE Rank2Types #-}
 
 -----------------------------------------------------------------------------
@@ -34,12 +35,18 @@
 import Data.Foldable (Foldable(foldr))
 import Data.Functor.Alt (Alt((<!>)))
 import Data.Functor.Apply (Apply ((<.>)))
-import Data.Monoid (Monoid(mappend, mempty))
 import Data.Profunctor
-import Data.Semigroup (Semigroup((<>)))
-import Data.Traversable (Traversable(traverse))
 import Prelude hiding (foldr)
 
+#if !(MIN_VERSION_base(4,8,0))
+import Data.Monoid (Monoid(mappend, mempty))
+import Data.Traversable (Traversable(traverse))
+#endif
+
+#if !(MIN_VERSION_base(4,11,0))
+import Data.Semigroup (Semigroup((<>)))
+#endif
+
 -- | 'Validation' is 'Either' with a Left that is a 'Monoid'
 data Validation e a
   = Failure e
@@ -98,9 +105,11 @@
 
 instance Monoid e => Monoid (Validation e a) where
   mempty = Failure mempty
+#if !(MIN_VERSION_base(4,11,0))
   x@Success{} `mappend` _ = x
   _ `mappend` x@Success{} = x
   Failure e1 `mappend` Failure e2 = Failure (e1 `mappend` e2)
+#endif
 
 type Prism s t a b = forall p f. (Choice p, Applicative f) => p a (f b) -> p s (f t)