diff --git a/.travis.yml b/.travis.yml
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,22 +1,23 @@
 # This Travis job script has been generated by a script via
 #
-#   haskell-ci '--config' 'cabal.haskell-ci' '--output' '.travis.yml' 'quadratic-irrational.cabal'
+#   haskell-ci 'quadratic-irrational.cabal'
 #
 # For more information, see https://github.com/haskell-CI/haskell-ci
 #
-# version: 0.2.1
+# version: 0.9.20200321
 #
+version: ~> 1.0
 language: c
+os: linux
 dist: xenial
-
 git:
-  submodules: false  # whether to recursively clone submodules
-
+  # whether to recursively clone submodules
+  submodules: false
 cache:
   directories:
     - $HOME/.cabal/packages
     - $HOME/.cabal/store
-
+    - $HOME/.hlint
 before_cache:
   - rm -fv $CABALHOME/packages/hackage.haskell.org/build-reports.log
   # remove files that are regenerated by 'cabal update'
@@ -25,110 +26,133 @@
   - 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:
+jobs:
   include:
-    - compiler: "ghc-8.8.1"
-      env: GHCHEAD=true
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.4,ghc-8.8.1], sources: [hvr-ghc]}}
-    - compiler: "ghc-8.6.5"
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.4,ghc-8.6.5], sources: [hvr-ghc]}}
-    - compiler: "ghc-8.4.4"
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.4,ghc-8.4.4], sources: [hvr-ghc]}}
-    - compiler: "ghc-8.2.2"
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.4,ghc-8.2.2], sources: [hvr-ghc]}}
-    - compiler: "ghc-8.0.2"
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.4,ghc-8.0.2], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.10.3"
-      env: TEST=--disable-tests
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-7.10.3], sources: [hvr-ghc]}}
-    - compiler: "ghc-head"
-      env: GHCHEAD=true
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-head], sources: [hvr-ghc]}}
-
+    - compiler: ghc-8.10.1
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.10.1","cabal-install-3.2"]}}
+      os: linux
+    - compiler: ghc-8.8.3
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.8.3","cabal-install-3.0"]}}
+      os: linux
+    - compiler: ghc-8.6.5
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.6.5","cabal-install-3.0"]}}
+      os: linux
+    - compiler: ghc-8.4.3
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.4.3","cabal-install-3.0"]}}
+      os: linux
+    - compiler: ghc-8.2.2
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.2.2","cabal-install-3.0"]}}
+      os: linux
+    - compiler: ghc-8.0.2
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.0.2","cabal-install-3.0"]}}
+      os: linux
   allow_failures:
-    - compiler: "ghc-8.8.1"
-    - compiler: "ghc-head"
-
+    - compiler: ghc-8.10.1
 before_install:
-  - HC=/opt/ghc/bin/${CC}
-  - HCPKG=${HC/ghc/ghc-pkg}
+  - HC=$(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:$PATH"
-  - ROOTDIR=$(pwd)
-  - HCNUMVER=$(( $(${HC} --numeric-version|sed -E 's/([0-9]+)\.([0-9]+)\.([0-9]+).*/\1 * 10000 + \2 * 100 + \3/') ))
+  - 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"
+  - set -o pipefail
+  - TEST=--enable-tests
+  - BENCH=--enable-benchmarks
+  - HEADHACKAGE=false
+  - if [ $HCNUMVER -ge 81000 ] ; 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
 install:
   - ${CABAL} --version
   - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
-  - TEST=${TEST---enable-tests}
-  - BENCH=--enable-benchmarks
-  - GHCHEAD=${GHCHEAD-false}
-  - travis_retry ${CABAL} update -v
-  - sed -i.bak 's/^jobs:/-- jobs:/' $CABALHOME/config
-  - rm -fv cabal.project cabal.project.local
   - |
-    if $GHCHEAD; then
-      sed -i.bak 's/-- allow-newer:.*/allow-newer: *:base, *:template-haskell, *:ghc, *:Cabal/' $CABALHOME/config
-    fi
-  - grep -Ev -- '^\s*--' $CABALHOME/config | grep -Ev '^\s*$'
-  - rm -f cabal.project
+    echo "program-default-options"                >> $CABALHOME/config
+    echo "  ghc-options: $GHCJOBS +RTS -M6G -RTS" >> $CABALHOME/config
+  - 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
-  - "printf 'packages: \".\"\\n' >> cabal.project"
-  - "printf 'write-ghc-environment-files: always\\n' >> cabal.project"
-  - touch cabal.project.local
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | grep -vE -- '^(quadratic-irrational)$' | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
+  - |
+    echo "packages: ." >> cabal.project
+  - |
+  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(quadratic-irrational)$' || true) | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
   - cat cabal.project || true
   - cat cabal.project.local || true
   - if [ -f "./configure.ac" ]; then (cd "." && autoreconf -i); fi
-  - rm -f cabal.project.freeze
-  - ${CABAL} new-freeze -w ${HC} ${TEST} ${BENCH} --project-file="cabal.project" --dry
-  - "cat \"cabal.project.freeze\" | sed -E 's/^(constraints: *| *)//' | sed 's/any.//'"
-  - rm  "cabal.project.freeze"
-  - ${CABAL} new-build -w ${HC} ${TEST} ${BENCH} --project-file="cabal.project" --dep -j2 all
-  - ${CABAL} new-build -w ${HC} --disable-tests --disable-benchmarks --project-file="cabal.project" --dep -j2 all
-  - rm -rf .ghc.environment.* "."/dist
-  - DISTDIR=$(mktemp -d /tmp/dist-test.XXXX)
-
-# Here starts the actual work to be performed for the package under test;
-# any command which exits with a non-zero exit code causes the build to fail.
+  - ${CABAL} v2-freeze $WITHCOMPILER ${TEST} ${BENCH}
+  - "cat cabal.project.freeze | sed -E 's/^(constraints: *| *)//' | sed 's/any.//'"
+  - rm  cabal.project.freeze
+  - travis_wait 40 ${CABAL} v2-build $WITHCOMPILER ${TEST} ${BENCH} --dep -j2 all
+  - travis_wait 40 ${CABAL} v2-build $WITHCOMPILER --disable-tests --disable-benchmarks --dep -j2 all
 script:
-  # test that source-distributions can be generated
-  - ${CABAL} new-sdist all
+  - DISTDIR=$(mktemp -d /tmp/dist-test.XXXX)
+  # Packaging...
+  - ${CABAL} v2-sdist all
+  # Unpacking...
   - mv dist-newstyle/sdist/*.tar.gz ${DISTDIR}/
   - cd ${DISTDIR} || false
-  - find . -maxdepth 1 -name '*.tar.gz' -exec tar -xvf '{}' \;
-  - rm -f cabal.project
+  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec tar -xvf '{}' \;
+  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec rm       '{}' \;
+  - PKGDIR_quadratic_irrational="$(find . -maxdepth 1 -type d -regex '.*/quadratic-irrational-[0-9.]*')"
+  # Generate cabal.project
+  - rm -rf cabal.project cabal.project.local cabal.project.freeze
   - touch cabal.project
-  - "printf 'packages: \"quadratic-irrational-*/*.cabal\"\\n' >> cabal.project"
-  - "printf 'write-ghc-environment-files: always\\n' >> cabal.project"
-  - touch cabal.project.local
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | grep -vE -- '^(quadratic-irrational)$' | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
+  - |
+    echo "packages: ${PKGDIR_quadratic_irrational}" >> cabal.project
+  - |
+  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(quadratic-irrational)$' || true) | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
   - cat cabal.project || true
   - cat cabal.project.local || true
+  # Building...
   # this builds all libraries and executables (without tests/benchmarks)
-  - ${CABAL} new-build -w ${HC} --disable-tests --disable-benchmarks all
-
+  - ${CABAL} v2-build $WITHCOMPILER --disable-tests --disable-benchmarks all
+  # Building with tests and benchmarks...
   # build & run tests, build benchmarks
-  - ${CABAL} new-build -w ${HC} ${TEST} ${BENCH} all
-  - if [ "x$TEST" = "x--enable-tests" ]; then ${CABAL} new-test -w ${HC} ${TEST} ${BENCH} all; fi
-
-  # cabal check
-  - (cd quadratic-irrational-* && ${CABAL} check)
-
-  # haddock
-  - ${CABAL} new-haddock -w ${HC} ${TEST} ${BENCH} all
-
-  # Build without installed constraints for packages in global-db
-  - rm -f cabal.project.local; ${CABAL} new-build -w ${HC} --disable-tests --disable-benchmarks all;
-
-  # Constraint sets
-  - rm -rf cabal.project.local
+  - ${CABAL} v2-build $WITHCOMPILER ${TEST} ${BENCH} all
+  # Testing...
+  - ${CABAL} v2-test $WITHCOMPILER ${TEST} ${BENCH} all
+  # cabal check...
+  - (cd ${PKGDIR_quadratic_irrational} && ${CABAL} -vnormal check)
+  # haddock...
+  - ${CABAL} v2-haddock $WITHCOMPILER --with-haddock $HADDOCK ${TEST} ${BENCH} all
+  # Building without installed constraints for packages in global-db...
+  - rm -f cabal.project.local
+  - ${CABAL} v2-build $WITHCOMPILER --disable-tests --disable-benchmarks all
 
-# REGENDATA ["--config","cabal.haskell-ci","--output",".travis.yml","quadratic-irrational.cabal"]
+# REGENDATA ("0.9.20200321",["quadratic-irrational.cabal"])
 # EOF
diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+# 0.1.1 (2020-04-15)
+
+* Support `arithmoi-0.11`.
+
 # 0.1.0 (2019-04-26)
 
 * Allow imaginary square roots, e. g., `qi 1 1 (-5) 1`.
diff --git a/quadratic-irrational.cabal b/quadratic-irrational.cabal
--- a/quadratic-irrational.cabal
+++ b/quadratic-irrational.cabal
@@ -1,6 +1,6 @@
 name: quadratic-irrational
 category: Math, Algorithms, Data
-version: 0.1.0
+version: 0.1.1
 license: MIT
 license-file: LICENSE
 author: Johan Kiviniemi <devel@johan.kiviniemi.name>
@@ -51,7 +51,7 @@
   > 3.5      = [3; 2]
   > (1+√5)/2 = [1; 1, 1, 1, …]
   > √2       = [1; 2, 2, 2, …]
-tested-with: GHC==7.10.3, GHC==8.0.2, GHC==8.2.2, GHC==8.4.3, GHC==8.6.5, GHC==8.8.1
+tested-with: GHC==8.0.2, GHC==8.2.2, GHC==8.4.3, GHC==8.6.5, GHC==8.8.3, GHC==8.10.1
 
 build-type: Simple
 cabal-version: >= 1.10
@@ -72,9 +72,10 @@
   other-modules:   Numeric.QuadraticIrrational.SquareFree
                  , Numeric.QuadraticIrrational.Ring
   hs-source-dirs: src
-  build-depends: base >= 4.8 && < 5
-               , arithmoi >= 0.7
+  build-depends: base >= 4.9 && < 5
+               , arithmoi >= 0.9
                , containers >= 0.5 && < 0.7
+               , integer-roots >= 1.0
                , transformers >= 0.3 && < 0.6
   if impl(ghc <8.0)
     build-depends:
diff --git a/src/Numeric/QuadraticIrrational.hs b/src/Numeric/QuadraticIrrational.hs
--- a/src/Numeric/QuadraticIrrational.hs
+++ b/src/Numeric/QuadraticIrrational.hs
@@ -81,8 +81,8 @@
 import Data.Semigroup
 import qualified Data.Set as Set (empty, insert, member)
 import Data.Type.Equality
-import Math.NumberTheory.Powers.Squares (integerSquareRoot)
-import Math.NumberTheory.Primes.Factorisation (factorise)
+import Math.NumberTheory.Primes (Prime, unPrime, factorise)
+import Math.NumberTheory.Roots (integerSquareRoot)
 import Text.Read (Lexeme (Ident), Read (readListPrec, readPrec),
   lexP, parens, prec, readListPrecDefault, step)
 
@@ -189,12 +189,10 @@
   case foldl' go (1,1) (factorise (abs c)) of
     ~(bMul, c') -> (b*bMul, c' * signum c)
   where
-    go :: Integral a => (Integer, Integer) -> (Integer, a) -> (Integer, Integer)
-    go ~(i, j) ~(fac, pow) =
-      i `seq` j `seq` fac `seq` pow `seq`
-        if even pow
-          then (i*fac^(pow     `div` 2), j)
-          else (i*fac^((pow-1) `div` 2), j*fac)
+    go :: (Integer, Integer) -> (Prime Integer, Word) -> (Integer, Integer)
+    go ~(i, j) ~(p, pow) =
+      i `seq` j `seq` p `seq` pow `seq`
+        (i * unPrime p ^ (pow `div` 2), if even pow then j else j * unPrime p)
 
 -- Reduce the @a@, @b@, @d@ factors before constructing a 'QI'.
 reduceCons :: Integer -> Integer -> Integer -> Integer -> QI