diff --git a/.travis.yml b/.travis.yml
--- a/.travis.yml
+++ b/.travis.yml
@@ -28,15 +28,15 @@
     - env: CABALVER=1.24 GHCVER=8.0.2
       compiler: ": #GHC 8.0.2"
       addons: {apt: {packages: [cabal-install-1.24,ghc-8.0.2], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=8.2.1
+    - env: CABALVER=2.0 GHCVER=8.2.1
       compiler: ": #GHC 8.2.1"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-8.2.1], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=head
+      addons: {apt: {packages: [cabal-install-2.0,ghc-8.2.1], sources: [hvr-ghc]}}
+    - env: CABALVER=head GHCVER=head
       compiler: ": #GHC head"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-head], sources: [hvr-ghc]}}
+      addons: {apt: {packages: [cabal-install-head,ghc-head], sources: [hvr-ghc]}}
 
   allow_failures:
-    - env: CABALVER=1.24 GHCVER=head
+    - env: CABALVER=head GHCVER=head
 
 before_install:
  - unset CC
diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,9 @@
+0.6.3
+-----
+* Add `Semigroup` instance for `Is`
+* Add `MonadFail` instance for `PlanT`
+* Support `doctest-0.12`
+
 0.6.2
 -----
 * Revamp `Setup.hs` to use `cabal-doctest`. This makes it build
diff --git a/Setup.lhs b/Setup.lhs
--- a/Setup.lhs
+++ b/Setup.lhs
@@ -1,182 +1,34 @@
 \begin{code}
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE OverloadedStrings #-}
+{-# 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 )
-#else
 
--- Otherwise we provide a shim
-
-#ifndef MIN_VERSION_Cabal
-#define MIN_VERSION_Cabal(x,y,z) 0
-#endif
-#ifndef MIN_VERSION_directory
-#define MIN_VERSION_directory(x,y,z) 0
-#endif
-#if MIN_VERSION_Cabal(1,24,0)
-#define InstalledPackageId UnitId
-#endif
-
-import Control.Monad ( when )
-import Data.List ( nub )
-import Data.String ( fromString )
-import Distribution.Package ( InstalledPackageId )
-import Distribution.Package ( PackageId, Package (..), packageVersion )
-import Distribution.PackageDescription ( PackageDescription(), TestSuite(..) , Library (..), BuildInfo (..))
-import Distribution.Simple ( defaultMainWithHooks, UserHooks(..), simpleUserHooks )
-import Distribution.Simple.Utils ( rewriteFile, createDirectoryIfMissingVerbose )
-import Distribution.Simple.BuildPaths ( autogenModulesDir )
-import Distribution.Simple.Setup ( BuildFlags(buildDistPref, buildVerbosity), fromFlag)
-import Distribution.Simple.LocalBuildInfo ( withPackageDB, withLibLBI, withTestLBI, LocalBuildInfo(), ComponentLocalBuildInfo(componentPackageDeps), compiler )
-import Distribution.Simple.Compiler ( showCompilerId , PackageDB (..))
-import Distribution.Text ( display , simpleParse )
-import System.FilePath ( (</>) )
-
-#if MIN_VERSION_Cabal(1,25,0)
-import Distribution.Simple.BuildPaths ( autogenComponentModulesDir )
-#endif
+import Distribution.Extra.Doctest ( defaultMainWithDoctests )
+main :: IO ()
+main = defaultMainWithDoctests "doctests"
 
-#if MIN_VERSION_directory(1,2,2)
-import System.Directory (makeAbsolute)
 #else
-import System.Directory (getCurrentDirectory)
-import System.FilePath (isAbsolute)
 
-makeAbsolute :: FilePath -> IO FilePath
-makeAbsolute p | isAbsolute p = return p
-               | otherwise    = do
-    cwd <- getCurrentDirectory
-    return $ cwd </> p
-#endif
-
-generateBuildModule :: String -> BuildFlags -> PackageDescription -> LocalBuildInfo -> IO ()
-generateBuildModule testsuiteName flags pkg lbi = do
-  let verbosity = fromFlag (buildVerbosity flags)
-  let distPref = fromFlag (buildDistPref flags)
-
-  -- Package DBs
-  let dbStack = withPackageDB lbi ++ [ SpecificPackageDB $ distPref </> "package.conf.inplace" ]
-  let dbFlags = "-hide-all-packages" : packageDbArgs dbStack
-
-  withLibLBI pkg lbi $ \lib libcfg -> do
-    let libBI = libBuildInfo lib
-
-    -- modules
-    let modules = exposedModules lib ++ otherModules libBI
-    -- it seems that doctest is happy to take in module names, not actual files!
-    let module_sources = modules
-
-    -- We need the directory with library's cabal_macros.h!
-#if MIN_VERSION_Cabal(1,25,0)
-    let libAutogenDir = autogenComponentModulesDir lbi libcfg
-#else
-    let libAutogenDir = autogenModulesDir lbi
+#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
 
-    -- Lib sources and includes
-    iArgs <- mapM (fmap ("-i"++) . makeAbsolute) $ libAutogenDir : hsSourceDirs libBI
-    includeArgs <- mapM (fmap ("-I"++) . makeAbsolute) $ includeDirs libBI
-
-    -- CPP includes, i.e. include cabal_macros.h
-    let cppFlags = map ("-optP"++) $
-            [ "-include", libAutogenDir ++ "/cabal_macros.h" ]
-            ++ cppOptions libBI
-
-    withTestLBI pkg lbi $ \suite suitecfg -> when (testName suite == fromString testsuiteName) $ do
-
-      -- get and create autogen dir
-#if MIN_VERSION_Cabal(1,25,0)
-      let testAutogenDir = autogenComponentModulesDir lbi suitecfg
-#else
-      let testAutogenDir = autogenModulesDir lbi
-#endif
-      createDirectoryIfMissingVerbose verbosity True testAutogenDir
-
-      -- write autogen'd file
-      rewriteFile (testAutogenDir </> "Build_doctests.hs") $ unlines
-        [ "module Build_doctests where"
-        , ""
-        -- -package-id etc. flags
-        , "pkgs :: [String]"
-        , "pkgs = " ++ (show $ formatDeps $ testDeps libcfg suitecfg)
-        , ""
-        , "flags :: [String]"
-        , "flags = " ++ show (iArgs ++ includeArgs ++ dbFlags ++ cppFlags)
-        , ""
-        , "module_sources :: [String]"
-        , "module_sources = " ++ show (map display module_sources)
-        ]
-  where
-    -- we do this check in Setup, as then doctests don't need to depend on Cabal
-    isOldCompiler = maybe False id $ do
-      a <- simpleParse $ showCompilerId $ compiler lbi
-      b <- simpleParse "7.5"
-      return $ packageVersion (a :: PackageId) < b
-
-    formatDeps = map formatOne
-    formatOne (installedPkgId, pkgId)
-      -- The problem is how different cabal executables handle package databases
-      -- when doctests depend on the library
-      | packageId pkg == pkgId = "-package=" ++ display pkgId
-      | otherwise              = "-package-id=" ++ display installedPkgId
-
-    -- From Distribution.Simple.Program.GHC
-    packageDbArgs :: [PackageDB] -> [String]
-    packageDbArgs | isOldCompiler = packageDbArgsConf
-                  | otherwise     = packageDbArgsDb
-
-    -- GHC <7.6 uses '-package-conf' instead of '-package-db'.
-    packageDbArgsConf :: [PackageDB] -> [String]
-    packageDbArgsConf dbstack = case dbstack of
-      (GlobalPackageDB:UserPackageDB:dbs) -> concatMap specific dbs
-      (GlobalPackageDB:dbs)               -> ("-no-user-package-conf")
-                                           : concatMap specific dbs
-      _ -> ierror
-      where
-        specific (SpecificPackageDB db) = [ "-package-conf=" ++ db ]
-        specific _                      = ierror
-        ierror = error $ "internal error: unexpected package db stack: "
-                      ++ show dbstack
-
-    -- GHC >= 7.6 uses the '-package-db' flag. See
-    -- https://ghc.haskell.org/trac/ghc/ticket/5977.
-    packageDbArgsDb :: [PackageDB] -> [String]
-    -- special cases to make arguments prettier in common scenarios
-    packageDbArgsDb dbstack = case dbstack of
-      (GlobalPackageDB:UserPackageDB:dbs)
-        | all isSpecific dbs              -> concatMap single dbs
-      (GlobalPackageDB:dbs)
-        | all isSpecific dbs              -> "-no-user-package-db"
-                                           : concatMap single dbs
-      dbs                                 -> "-clear-package-db"
-                                           : concatMap single dbs
-     where
-       single (SpecificPackageDB db) = [ "-package-db=" ++ db ]
-       single GlobalPackageDB        = [ "-global-package-db" ]
-       single UserPackageDB          = [ "-user-package-db" ]
-       isSpecific (SpecificPackageDB _) = True
-       isSpecific _                     = False
-
-testDeps :: ComponentLocalBuildInfo -> ComponentLocalBuildInfo -> [(InstalledPackageId, PackageId)]
-testDeps xs ys = nub $ componentPackageDeps xs ++ componentPackageDeps ys
+import Distribution.Simple
 
-defaultMainWithDoctests :: String -> IO ()
-defaultMainWithDoctests testSuiteName = defaultMainWithHooks simpleUserHooks
-  { buildHook = \pkg lbi hooks flags -> do
-     generateBuildModule testSuiteName flags pkg lbi
-     buildHook simpleUserHooks pkg lbi hooks flags
-  }
+main :: IO ()
+main = defaultMain
 
 #endif
-
-main :: IO ()
-main = defaultMainWithDoctests "doctests"
 
 \end{code}
diff --git a/Warning.hs b/Warning.hs
new file mode 100644
--- /dev/null
+++ b/Warning.hs
@@ -0,0 +1,5 @@
+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/machines.cabal b/machines.cabal
--- a/machines.cabal
+++ b/machines.cabal
@@ -1,6 +1,6 @@
 name:          machines
 category:      Control, Enumerator
-version:       0.6.2
+version:       0.6.3
 license:       BSD3
 cabal-version: >= 1.10
 license-file:  LICENSE
@@ -25,6 +25,7 @@
   config
   README.markdown
   CHANGELOG.markdown
+  Warning.hs
   examples/LICENSE
   examples/machines-examples.cabal
   examples/*.hs
@@ -83,6 +84,13 @@
     UndecidableInstances
 
   ghc-options: -Wall -fwarn-tabs -O2 -fdicts-cheap -funbox-strict-fields
+
+  -- See https://ghc.haskell.org/trac/ghc/wiki/Migration/8.0#base-4.9.0.0
+  if impl(ghc >= 8.0)
+    ghc-options: -Wcompat -Wnoncanonical-monad-instances -Wnoncanonical-monadfail-instances
+  else
+    build-depends: fail == 4.9.*
+
   hs-source-dirs: src
 
 -- Verify the results of the examples
@@ -92,7 +100,8 @@
   default-language: Haskell2010
   build-depends:
     base    == 4.*,
-    doctest >= 0.11.1 && < 0.12
+    doctest >= 0.11.1 && < 0.13,
+    machines
   ghc-options: -Wall -threaded
   hs-source-dirs: tests
 
@@ -107,7 +116,7 @@
     base                == 4.*,
     conduit             >= 1.0   && < 1.3,
     conduit-combinators >= 0.2.5 && < 1.2,
-    criterion           >= 0.6   && < 1.2,
+    criterion           >= 0.6   && < 1.3,
     machines,
     mtl                 >= 2     && < 2.3,
     pipes               >= 4     && < 4.4
diff --git a/src/Data/Machine/Is.hs b/src/Data/Machine/Is.hs
--- a/src/Data/Machine/Is.hs
+++ b/src/Data/Machine/Is.hs
@@ -15,7 +15,7 @@
   ) where
 
 import Control.Category
-import Data.Monoid
+import Data.Semigroup
 import Prelude
 
 -- | Witnessed type equality
@@ -33,10 +33,14 @@
   Refl `compare` Refl = EQ
   {-# INLINE compare #-}
 
+instance (a ~ b) => Semigroup (Is a b) where
+  Refl <> Refl = Refl
+  {-# INLINE (<>) #-}
+
 instance (a ~ b) => Monoid (Is a b) where
   mempty = Refl
   {-# INLINE mempty #-}
-  mappend Refl Refl = Refl
+  mappend = (<>)
   {-# INLINE mappend #-}
 
 instance (a ~ b) => Read (Is a b) where
diff --git a/src/Data/Machine/Mealy.hs b/src/Data/Machine/Mealy.hs
--- a/src/Data/Machine/Mealy.hs
+++ b/src/Data/Machine/Mealy.hs
@@ -95,12 +95,12 @@
 
 -- | slow diagonalization
 instance Monad (Mealy a) where
-  return b = r where r = Mealy (const (b, r))
+  return = pure
   {-# INLINE return #-}
   m >>= f = Mealy $ \a -> case runMealy m a of
     (b, m') -> (fst (runMealy (f b) a), m' >>= f)
   {-# INLINE (>>=) #-}
-  _ >> n = n
+  (>>) = (*>)
   {-# INLINE (>>) #-}
 
 instance Profunctor Mealy where
diff --git a/src/Data/Machine/MealyT.hs b/src/Data/Machine/MealyT.hs
--- a/src/Data/Machine/MealyT.hs
+++ b/src/Data/Machine/MealyT.hs
@@ -49,8 +49,12 @@
   MealyT m <*> MealyT n = MealyT $ \a -> (\(mb, mm) (nb, nm) -> (mb nb, mm <*> nm)) <$> m a <*> n a
 
 instance Monad m => Monad (MealyT m a) where
+#if !MIN_VERSION_base(4,8,0)
+  -- pre-AMP
   {-# INLINE return #-}
   return b = r where r = MealyT (const (return (b, r))) -- Stolen from Pointed
+#endif
+
   MealyT g >>= f = MealyT $ \a ->
     do (b, MealyT _h) <- g a
        runMealyT (f b) a
diff --git a/src/Data/Machine/Moore.hs b/src/Data/Machine/Moore.hs
--- a/src/Data/Machine/Moore.hs
+++ b/src/Data/Machine/Moore.hs
@@ -98,11 +98,11 @@
 
 -- | slow diagonalization
 instance Monad (Moore a) where
-  return a = r where r = Moore a (const r)
+  return = pure
   {-# INLINE return #-}
   k >>= f = j (fmap f k) where
     j (Moore a g) = Moore (extract a) (\x -> j $ fmap (\(Moore _ h) -> h x) (g x))
-  _ >> m = m
+  (>>) = (*>)
 
 instance Copointed (Moore a) where
   copoint (Moore b _) = b
diff --git a/src/Data/Machine/Plan.hs b/src/Data/Machine/Plan.hs
--- a/src/Data/Machine/Plan.hs
+++ b/src/Data/Machine/Plan.hs
@@ -39,6 +39,7 @@
 import Control.Monad.State.Class
 import Control.Monad.Reader.Class
 import Control.Monad.Error.Class
+import qualified Control.Monad.Fail as Fail
 import Control.Monad.Writer.Class
 import Data.Functor.Identity
 import Prelude hiding ((.),id)
@@ -114,10 +115,13 @@
   return = pure
   {-# INLINE return #-}
   PlanT m >>= f = PlanT (\kp ke kr kf -> m (\a -> runPlanT (f a) kp ke kr kf) ke kr kf)
+  {-# INLINE (>>=) #-}
   (>>) = (*>)
   {-# INLINE (>>) #-}
+  fail = Fail.fail
+
+instance Fail.MonadFail (PlanT k o m) where
   fail _ = PlanT (\_ _ _ kf -> kf)
-  {-# INLINE (>>=) #-}
 
 instance MonadPlus (PlanT k o m) where
   mzero = empty