diff --git a/.travis.yml b/.travis.yml
index 782df42..991b364 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,7 @@
 #
 #   runghc make_travis_yml_2.hs '-o' '.travis.yml' 'xmonad.cabal' 'libxrandr-dev'
 #
-# For more information, see https://github.com/hvr/multi-ghc-travis
+# For more information, see https://github.com/haskell-CI/haskell-ci
 #
 language: c
 sudo: false
@@ -28,6 +28,9 @@ before_cache:
 
 matrix:
   include:
+    - compiler: "ghc-8.6.1"
+      env: GHCHEAD=true
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-8.6.1,libxrandr-dev], sources: [hvr-ghc]}}
     - compiler: "ghc-8.4.3"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
       addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-8.4.3,libxrandr-dev], sources: [hvr-ghc]}}
@@ -37,15 +40,9 @@ matrix:
     - compiler: "ghc-8.0.2"
     # env: TEST=--disable-tests BENCH=--disable-benchmarks
       addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-8.0.2,libxrandr-dev], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.10.3"
-    # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.10.3,libxrandr-dev], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.8.4"
-    # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.8.4,libxrandr-dev], sources: [hvr-ghc]}}
-    - compiler: "ghc-7.6.3"
-    # env: TEST=--disable-tests BENCH=--disable-benchmarks
-      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.2,ghc-7.6.3,libxrandr-dev], sources: [hvr-ghc]}}
+
+  allow_failures:
+    - compiler: "ghc-8.6.1"
 
 before_install:
   - HC=${CC}
@@ -69,6 +66,24 @@ install:
   - travis_retry cabal update -v
   - "sed -i.bak 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config"
   - rm -fv cabal.project cabal.project.local
+  # Overlay Hackage Package Index for GHC HEAD: https://github.com/hvr/head.hackage
+  - |
+    if $GHCHEAD; then
+      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
+      echo '   secure: True'                                                                >> ${HOME}/.cabal/config
+      echo '   root-keys: 07c59cb65787dedfaef5bd5f987ceb5f7e5ebf88b904bbd4c5cbdeb2ff71b740' >> ${HOME}/.cabal/config
+      echo '              2e8555dde16ebd8df076f1a8ef13b8f14c66bad8eafefd7d9e37d0ed711821fb' >> ${HOME}/.cabal/config
+      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"
   - touch cabal.project.local
diff --git a/CHANGES.md b/CHANGES.md
index 05fdaae..cff04c7 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -11,6 +11,15 @@
     and to install them into proper locations where their users expect them.
     [https://github.com/xmonad/xmonad/pull/127]
 
+### Bug Fixes
+
+  * Add support for GHC 8.6.x by providing an instance for 'MonadFail X'. A
+    side effect of that change is that our code no longer compiles with GHC
+    versions prior to 8.0.x. We could work around that, no doubt, but the
+    resulting code would require CPP and Cabal flags and whatnot. It feels more
+    reasonable to just require a moderately recent compiler instead of going
+    through all that trouble.
+
 ## 0.14 (July 30, 2018)
 
 ### Bug Fixes
diff --git a/src/XMonad/Core.hs b/src/XMonad/Core.hs
index 3c891ea..5333696 100644
--- a/src/XMonad/Core.hs
+++ b/src/XMonad/Core.hs
@@ -37,6 +37,7 @@ import Prelude
 import Control.Exception.Extensible (fromException, try, bracket, throw, finally, SomeException(..))
 import qualified Control.Exception.Extensible as E
 import Control.Applicative(Applicative, pure, (<$>), (<*>))
+import Control.Monad.Fail
 import Control.Monad.State
 import Control.Monad.Reader
 import Data.Semigroup
@@ -147,7 +148,7 @@ data ScreenDetail   = SD { screenRect :: !Rectangle } deriving (Eq,Show, Read)
 -- instantiated on 'XConf' and 'XState' automatically.
 --
 newtype X a = X (ReaderT XConf (StateT XState IO) a)
-    deriving (Functor, Monad, MonadIO, MonadState XState, MonadReader XConf, Typeable)
+    deriving (Functor, Monad, MonadFail, MonadIO, MonadState XState, MonadReader XConf, Typeable)
 
 instance Applicative X where
   pure = return
diff --git a/xmonad.cabal b/xmonad.cabal
index 8a16c25..e41d144 100644
--- a/xmonad.cabal
+++ b/xmonad.cabal
@@ -28,13 +28,7 @@ cabal-version:      >= 1.8
 bug-reports:        https://github.com/xmonad/xmonad/issues
 build-type:         Simple
 
-tested-with:
-                    GHC==7.6.3,
-                    GHC==7.8.4,
-                    GHC==7.10.3,
-                    GHC==8.0.2,
-                    GHC==8.2.2,
-                    GHC==8.4.3
+tested-with:        GHC==8.0.2, GHC==8.2.2, GHC==8.4.3, GHC==8.6.1
 
 source-repository head
   type:     git
@@ -62,7 +56,7 @@ library
                         XMonad.StackSet
     other-modules:      Paths_xmonad
 
-    build-depends: base >= 4.6 && < 4.12,
+    build-depends: base >= 4.6 && < 5,
                    containers,
                    data-default,
                    directory,
@@ -86,6 +80,8 @@ library
         -- needed for XMonad.Config's instance Default (XConfig a)
     if flag(testing)
         buildable: False
+    if !impl(ghc > 8)
+        build-depends: fail
 
 executable xmonad
     main-is:        Main.hs