diff --git a/.travis.yml b/.travis.yml
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,6 @@
 # This Travis job script has been generated by a script via
 #
-#   runghc make_travis_yml_2.hs '-o' '.travis.yml' '--irc-channel=irc.freenode.org#haskell-lens' '--no-no-tests-no-bench' '--no-installed' 'cabal.project'
+#   runghc make_travis_yml_2.hs '-o' '.travis.yml' '--ghc-head' '--irc-channel=irc.freenode.org#haskell-lens' '--no-no-tests-no-bench' '--no-unconstrained' 'cabal.project'
 #
 # For more information, see https://github.com/hvr/multi-ghc-travis
 #
@@ -36,42 +36,45 @@
 
 matrix:
   include:
-    - compiler: "ghc-7.0.4"
+    - compiler: "ghc-8.6.1"
+      env: GHCHEAD=true
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-8.6.1], sources: [hvr-ghc]}}
+    - compiler: "ghc-8.4.3"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.0.4], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.2.2"
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-8.4.3], sources: [hvr-ghc]}}
+    - compiler: "ghc-8.2.2"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.2.2], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.4.2"
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-8.2.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-8.0.2"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.4.2], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.6.3"
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-8.0.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.10.3"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.6.3], sources: [hvr-ghc]}}
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.10.3], sources: [hvr-ghc]}}
     - compiler: "ghc-7.8.4"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.8.4], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.10.3"
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.8.4], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.6.3"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.10.3], sources: [hvr-ghc]}}
-    - compiler: "ghc-8.0.2"
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.6.3], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.4.2"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-8.0.2], sources: [hvr-ghc]}}
-    - compiler: "ghc-8.2.2"
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.4.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.2.2"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-8.2.2], sources: [hvr-ghc]}}
-    - compiler: "ghc-8.4.1"
-      env: GHCHEAD=true
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-8.4.1], sources: [hvr-ghc]}}
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.2.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.0.4"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.0.4], sources: [hvr-ghc]}}
     - compiler: "ghc-head"
       env: GHCHEAD=true
       addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-head], sources: [hvr-ghc]}}
 
   allow_failures:
+    - compiler: "ghc-head"
     - compiler: "ghc-7.0.4"
     - compiler: "ghc-7.2.2"
-    - compiler: "ghc-8.4.1"
-    - compiler: "ghc-head"
+    - compiler: "ghc-8.6.1"
 
 before_install:
   - HC=${CC}
@@ -89,7 +92,8 @@
   - BENCH=${BENCH---enable-benchmarks}
   - TEST=${TEST---enable-tests}
   - HADDOCK=${HADDOCK-true}
-  - INSTALLED=${INSTALLED-true}
+  - UNCONSTRAINED=${UNCONSTRAINED-true}
+  - NOINSTALLEDCONSTRAINTS=${NOINSTALLEDCONSTRAINTS-false}
   - GHCHEAD=${GHCHEAD-false}
   - travis_retry cabal update -v
   - "sed -i.bak 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config"
@@ -97,7 +101,8 @@
   # Overlay Hackage Package Index for GHC HEAD: https://github.com/hvr/head.hackage
   - |
     if $GHCHEAD; then
-      sed -i.bak 's/-- allow-newer:.*/allow-newer: *:base, *:template-haskell, *:ghc, *:Cabal/' ${HOME}/.cabal/config
+      sed -i 's/-- allow-newer: .*/allow-newer: *:base/' ${HOME}/.cabal/config
+      for pkg in $($HCPKG list --simple-output); do pkg=$(echo $pkg | sed 's/-[^-]*$//'); sed -i "s/allow-newer: /allow-newer: *:$pkg, /" ${HOME}/.cabal/config; done
 
       echo 'repository head.hackage'                                                        >> ${HOME}/.cabal/config
       echo '   url: http://head.hackage.haskell.org/'                                       >> ${HOME}/.cabal/config
@@ -107,17 +112,22 @@
       echo '              8f79fd2389ab2967354407ec852cbe73f2e8635793ac446d09461ffb99527f6e' >> ${HOME}/.cabal/config
       echo '   key-threshold: 3'                                                            >> ${HOME}/.cabal.config
 
+      grep -Ev -- '^\s*--' ${HOME}/.cabal/config | grep -Ev '^\s*$'
+
       cabal new-update head.hackage -v
     fi
   - grep -Ev -- '^\s*--' ${HOME}/.cabal/config | grep -Ev '^\s*$'
   - "printf 'packages: \".\"\\n' > cabal.project"
-  - cat cabal.project
+  - touch cabal.project.local
+  - "if ! $NOINSTALLEDCONSTRAINTS; then for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/^/constraints: /' | sed 's/-[^-]*$/ installed/' >> cabal.project.local; done; fi"
+  - 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-build -w ${HC} ${TEST} ${BENCH} --project-file="cabal.project" --dep -j2 all
-  - rm -rf "."/.ghc.environment.* "."/dist
+  - rm -rf .ghc.environment.* "."/dist
   - DISTDIR=$(mktemp -d /tmp/dist-test.XXXX)
 
 # Here starts the actual work to be performed for the package under test;
@@ -129,8 +139,10 @@
   - cd ${DISTDIR} || false
   - find . -maxdepth 1 -name '*.tar.gz' -exec tar -xvf '{}' \;
   - "printf 'packages: semigroups-*/*.cabal\\n' > cabal.project"
-  - cat cabal.project
-
+  - touch cabal.project.local
+  - "if ! $NOINSTALLEDCONSTRAINTS; then for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/^/constraints: /' | sed 's/-[^-]*$/ installed/' >> cabal.project.local; done; fi"
+  - cat cabal.project || true
+  - cat cabal.project.local || true
 
   # build & run tests, build benchmarks
   - cabal new-build -w ${HC} ${TEST} ${BENCH} all
@@ -142,5 +154,5 @@
   - rm -rf ./dist-newstyle
   - if $HADDOCK; then cabal new-haddock -w ${HC} ${TEST} ${BENCH} all; else echo "Skipping haddock generation";fi
 
-# REGENDATA ["-o",".travis.yml","--irc-channel=irc.freenode.org#haskell-lens","--no-no-tests-no-bench","--no-installed","cabal.project"]
+# REGENDATA ["-o",".travis.yml","--ghc-head","--irc-channel=irc.freenode.org#haskell-lens","--no-no-tests-no-bench","--no-unconstrained","cabal.project"]
 # EOF
diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,8 @@
+0.18.5 [2018.07.02]
+-------------------
+* Use a more efficient `sconcat` for the `Semigroup` instances for strict and
+  lazy `ByteString`.
+
 0.18.4 [2018.01.29]
 -------------------
 * Backport `Semigroup` instances for `Data.Ord.Down` and strict `ST`, which were
diff --git a/semigroups.cabal b/semigroups.cabal
--- a/semigroups.cabal
+++ b/semigroups.cabal
@@ -1,6 +1,6 @@
 name:          semigroups
 category:      Algebra, Data, Data Structures, Math
-version:       0.18.4
+version:       0.18.5
 license:       BSD3
 cabal-version: >= 1.10
 license-file:  LICENSE
@@ -23,7 +23,8 @@
              , GHC == 7.10.3
              , GHC == 8.0.2
              , GHC == 8.2.2
-             , GHC == 8.4.1
+             , GHC == 8.4.3
+             , GHC == 8.6.1
 
 source-repository head
   type: git
@@ -150,7 +151,7 @@
         build-depends: bytestring         >= 0.10.4 && < 1
 
     if flag(containers)
-      build-depends: containers >= 0.3 && < 0.6
+      build-depends: containers >= 0.3 && < 0.7
 
     if flag(deepseq)
       build-depends: deepseq >= 1.1 && < 1.5
diff --git a/src-ghc7/Data/Semigroup.hs b/src-ghc7/Data/Semigroup.hs
--- a/src-ghc7/Data/Semigroup.hs
+++ b/src-ghc7/Data/Semigroup.hs
@@ -145,8 +145,8 @@
 #endif
 
 #ifdef MIN_VERSION_bytestring
-import Data.ByteString as Strict
-import Data.ByteString.Lazy as Lazy
+import Data.ByteString as BS
+import Data.ByteString.Lazy as BL
 
 # if (MIN_VERSION_bytestring(0,10,2)) || defined(MIN_VERSION_bytestring_builder)
 import qualified Data.ByteString.Builder as ByteString
@@ -172,8 +172,8 @@
 #endif
 
 #ifdef MIN_VERSION_text
-import qualified Data.Text as Strict
-import qualified Data.Text.Lazy as Lazy
+import qualified Data.Text as TS
+import qualified Data.Text.Lazy as TL
 import qualified Data.Text.Lazy.Builder as Text
 #endif
 
@@ -939,11 +939,13 @@
 #endif
 
 #ifdef MIN_VERSION_bytestring
-instance Semigroup Strict.ByteString where
+instance Semigroup BS.ByteString where
   (<>) = mappend
+  sconcat (b:|bs) = BS.concat (b:bs)
 
-instance Semigroup Lazy.ByteString where
+instance Semigroup BL.ByteString where
   (<>) = mappend
+  sconcat (b:|bs) = BL.concat (b:bs)
 
 # if (MIN_VERSION_bytestring(0,10,0)) || defined(MIN_VERSION_bytestring_builder)
 instance Semigroup ByteString.Builder where
@@ -957,10 +959,10 @@
 #endif
 
 #ifdef MIN_VERSION_text
-instance Semigroup Strict.Text where
+instance Semigroup TS.Text where
   (<>) = mappend
 
-instance Semigroup Lazy.Text where
+instance Semigroup TL.Text where
   (<>) = mappend
 
 instance Semigroup Text.Builder where
diff --git a/src/Data/Semigroup/Generic.hs b/src/Data/Semigroup/Generic.hs
--- a/src/Data/Semigroup/Generic.hs
+++ b/src/Data/Semigroup/Generic.hs
@@ -27,7 +27,9 @@
   , gmempty
   ) where
 
+#if !(MIN_VERSION_base(4,11,0))
 import Data.Semigroup
+#endif
 import GHC.Generics
 
 -- | Generically generate a 'Semigroup' ('<>') operation for any type