diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,13 @@
 Changes
 =======
 
+Version 0.12.0.1
+----------------
+
+Fix compatibility with GHC 8.4
+
 Version 0.12
---------------
+------------
 
 Backward compat breaking revision of `Test.Tasty.Ingredients.ConsoleReporter`
 that exposes the name of tests/groups.
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -16,18 +16,10 @@
 * Extensibility: add your own test providers and ingredients (runners) above and
   beyond those provided
 
-[![Build Status](https://travis-ci.org/feuerbach/tasty.png?branch=master)](https://travis-ci.org/feuerbach/tasty)
-
 To find out what's new, read the **[change log][]**.
 
 [change log]: https://github.com/feuerbach/tasty/blob/master/core/CHANGELOG.md
 
-Ask any tasty-related questions on the **[mailing list][]** or IRC channel
-**#tasty** at FreeNode ([logs & stats][ircbrowse]).
-
-[mailing list]: https://groups.google.com/forum/#!forum/haskell-tasty
-[ircbrowse]: http://ircbrowse.net/tasty
-
 ## Example
 
 Here's how your `test.hs` might look like:
@@ -111,6 +103,8 @@
   (based on [smallcheck](http://hackage.haskell.org/package/smallcheck))
 * [tasty-quickcheck](http://hackage.haskell.org/package/tasty-quickcheck) — for randomized
   property-based testing (based on [QuickCheck](http://hackage.haskell.org/package/QuickCheck))
+* [tasty-hedgehog](https://github.com/qfpl/tasty-hedgehog) — for randomized
+  property-based testing (based on [Hedgehog](http://hackage.haskell.org/package/hedgehog))
 * [tasty-hspec](http://hackage.haskell.org/package/tasty-hspec) — for
   [Hspec](http://hspec.github.io/) tests
 * [tasty-program](http://hackage.haskell.org/package/tasty-program) — run
@@ -415,26 +409,6 @@
 * [Code testing in Haskell revisited (with Tasty)](http://lambda.jstolarek.com/2014/01/code-testing-in-haskell-revisited-with-tasty/)
 
 [custom-options-article]: http://ro-che.info/articles/2013-12-20-tasty-custom-options.html
-
-## Background
-
-Tasty is heavily influenced by [test-framework][].
-
-The problems with test-framework are:
-
-* Poor code style (some lines of the code wouldn't even fit in a twitter message!)
-* Poor architecture — e.g. relying on laziness for IO and control flow. The
-  whole story with `:~>` and `ImprovingIO` is really obscure.
-* Non-extensible options. For example, when I integrated SmallCheck with
-  test-framework (in the form of the `test-framework-smallcheck` package), I
-  still had to submit patches to the main package to make SmallCheck depth
-  customizable by the user.
-* The project is effectively unmaintained.
-
-So I decided to recreate everything that I liked in test-framework from scratch
-in this package.
-
-[test-framework]: http://batterseapower.github.io/test-framework/
 
 Maintainers
 -----------
diff --git a/Test/Tasty/Core.hs b/Test/Tasty/Core.hs
--- a/Test/Tasty/Core.hs
+++ b/Test/Tasty/Core.hs
@@ -223,12 +223,12 @@
   -> TestTree
      -- ^ the tree to fold
   -> b
-foldTestTree (TreeFold fTest fGroup fResource) opts tree =
-  let pat = lookupOption opts
-  in go pat [] opts tree
+foldTestTree (TreeFold fTest fGroup fResource) opts0 tree0 =
+  let pat = lookupOption opts0
+  in go pat [] opts0 tree0
   where
-    go pat path opts tree =
-      case tree of
+    go pat path opts tree1 =
+      case tree1 of
         SingleTest name test
           | testPatternMatches pat (path ++ [name])
             -> fTest opts name test
@@ -236,7 +236,7 @@
         TestGroup name trees ->
           fGroup name $ foldMap (go pat (path ++ [name]) opts) trees
         PlusTestOptions f tree -> go pat path (f opts) tree
-        WithResource res tree -> fResource res $ \res -> go pat path opts (tree res)
+        WithResource res0 tree -> fResource res0 $ \res -> go pat path opts (tree res)
         AskOptions f -> go pat path opts (f opts)
 
 -- | Get the list of options that are relevant for a given test tree
diff --git a/Test/Tasty/Ingredients/ConsoleReporter.hs b/Test/Tasty/Ingredients/ConsoleReporter.hs
--- a/Test/Tasty/Ingredients/ConsoleReporter.hs
+++ b/Test/Tasty/Ingredients/ConsoleReporter.hs
@@ -22,11 +22,11 @@
   , foldTestOutput
   ) where
 
+import Prelude hiding (fail)
 import Control.Monad.State hiding (fail)
 import Control.Monad.Reader hiding (fail,reader)
 import Control.Concurrent.STM
 import Control.Exception
-import Control.Applicative
 import Test.Tasty.Core
 import Test.Tasty.Run
 import Test.Tasty.Ingredients
@@ -39,14 +39,20 @@
 import Data.Char
 import Data.Maybe
 import Data.Monoid
-import Data.Proxy
-import Data.Tagged
 import Data.Typeable
-import Data.Foldable hiding (concatMap,elem,sequence_)
-import Options.Applicative
-import Prelude hiding (fail)  -- Silence AMP and FTP import warnings
+import Options.Applicative hiding (str)
 import System.IO
 import System.Console.ANSI
+#if !MIN_VERSION_base(4,8,0)
+import Data.Proxy
+import Data.Tagged
+import Data.Foldable hiding (concatMap,elem,sequence_)
+import Control.Applicative
+#endif
+#if MIN_VERSION_base(4,9,0)
+import Data.Semigroup (Semigroup)
+import qualified Data.Semigroup (Semigroup((<>)))
+#endif
 
 --------------------------------------------------
 -- TestOutput base definitions
@@ -75,6 +81,10 @@
 instance Monoid TestOutput where
   mempty = Skip
   mappend = Seq
+#if MIN_VERSION_base(4,9,0)
+instance Semigroup TestOutput where
+  (<>) = mappend
+#endif
 
 type Level = Int
 
@@ -177,36 +187,36 @@
 --------------------------------------------------
 -- {{{
 consoleOutput :: (?colors :: Bool) => TestOutput -> StatusMap -> IO ()
-consoleOutput output smap =
-  getTraversal . fst $ foldTestOutput foldTest foldHeading output smap
+consoleOutput toutput smap =
+  getTraversal . fst $ foldTestOutput foldTest foldHeading toutput smap
   where
     foldTest _name printName getResult printResult =
       ( Traversal $ do
-          printName
+          printName :: IO ()
           r <- getResult
           printResult r
       , Any True)
     foldHeading _name printHeading (printBody, Any nonempty) =
       ( Traversal $ do
-          when nonempty $ do printHeading; getTraversal printBody
+          when nonempty $ do printHeading :: IO (); getTraversal printBody
       , Any nonempty
       )
 
 consoleOutputHidingSuccesses :: (?colors :: Bool) => TestOutput -> StatusMap -> IO ()
-consoleOutputHidingSuccesses output smap =
-  void . getApp $ foldTestOutput foldTest foldHeading output smap
+consoleOutputHidingSuccesses toutput smap =
+  void . getApp $ foldTestOutput foldTest foldHeading toutput smap
   where
     foldTest _name printName getResult printResult =
       Ap $ do
-          printName
+          printName :: IO ()
           r <- getResult
           if resultSuccessful r
             then do clearThisLine; return $ Any False
-            else do printResult r; return $ Any True
+            else do printResult r :: IO (); return $ Any True
 
     foldHeading _name printHeading printBody =
       Ap $ do
-        printHeading
+        printHeading :: IO ()
         Any failed <- getApp printBody
         unless failed clearAboveLine
         return $ Any failed
@@ -215,9 +225,9 @@
     clearThisLine = do clearLine; setCursorColumn 0
 
 streamOutputHidingSuccesses :: (?colors :: Bool) => TestOutput -> StatusMap -> IO ()
-streamOutputHidingSuccesses output smap =
+streamOutputHidingSuccesses toutput smap =
   void . flip evalStateT [] . getApp $
-    foldTestOutput foldTest foldHeading output smap
+    foldTestOutput foldTest foldHeading toutput smap
   where
     foldTest _name printName getResult printResult =
       Ap $ do
@@ -230,8 +240,8 @@
 
               liftIO $ do
                 sequence_ $ reverse stack
-                printName
-                printResult r
+                printName :: IO ()
+                printResult r :: IO ()
 
               return $ Any True
 
@@ -267,6 +277,10 @@
 instance Monoid Statistics where
   Statistics t1 f1 `mappend` Statistics t2 f2 = Statistics (t1 + t2) (f1 + f2)
   mempty = Statistics 0 0
+#if MIN_VERSION_base(4,9,0)
+instance Semigroup Statistics where
+  (<>) = mappend
+#endif
 
 computeStatistics :: StatusMap -> IO Statistics
 computeStatistics = getApp . foldMap (\var -> Ap $
@@ -391,14 +405,14 @@
             ?colors = useColor whenColor isTerm
 
           let
-            output = buildTestOutput opts tree
+            toutput = buildTestOutput opts tree
 
           case () of { _
             | hideSuccesses && isTerm ->
-                consoleOutputHidingSuccesses output smap
+                consoleOutputHidingSuccesses toutput smap
             | hideSuccesses && not isTerm ->
-                streamOutputHidingSuccesses output smap
-            | otherwise -> consoleOutput output smap
+                streamOutputHidingSuccesses toutput smap
+            | otherwise -> consoleOutput toutput smap
           }
 
           return $ \time -> do
@@ -447,8 +461,8 @@
 --
 --   @since 0.11.3
 useColor :: UseColor -> Bool -> Bool
-useColor when isTerm =
-  case when of
+useColor when_ isTerm =
+  case when_ of
     Never  -> False
     Always -> True
     Auto   -> isTerm
@@ -521,6 +535,10 @@
   Maximum a `mappend` Maximum b = Maximum (a `max` b)
   MinusInfinity `mappend` a = a
   a `mappend` MinusInfinity = a
+#if MIN_VERSION_base(4,9,0)
+instance Ord a => Semigroup (Maximum a) where
+  (<>) = mappend
+#endif
 
 -- | Compute the amount of space needed to align "OK"s and "FAIL"s
 computeAlignment :: OptionSet -> TestTree -> Int
diff --git a/Test/Tasty/Ingredients/ListTests.hs b/Test/Tasty/Ingredients/ListTests.hs
--- a/Test/Tasty/Ingredients/ListTests.hs
+++ b/Test/Tasty/Ingredients/ListTests.hs
@@ -1,5 +1,5 @@
 -- | Ingredient for listing test names
-{-# LANGUAGE GeneralizedNewtypeDeriving, DeriveDataTypeable #-}
+{-# LANGUAGE CPP, GeneralizedNewtypeDeriving, DeriveDataTypeable #-}
 module Test.Tasty.Ingredients.ListTests
   ( ListTests(..)
   , testsNames
@@ -8,8 +8,10 @@
 
 import Data.Proxy
 import Data.Typeable
-import Data.Monoid
 import Options.Applicative
+#if !MIN_VERSION_base(4,8,0)
+import Data.Monoid
+#endif
 
 import Test.Tasty.Core
 import Test.Tasty.Options
diff --git a/Test/Tasty/Options.hs b/Test/Tasty/Options.hs
--- a/Test/Tasty/Options.hs
+++ b/Test/Tasty/Options.hs
@@ -1,6 +1,6 @@
 {-# LANGUAGE ScopedTypeVariables, DeriveDataTypeable,
              ExistentialQuantification, GADTs,
-             OverlappingInstances, FlexibleInstances, UndecidableInstances,
+             FlexibleInstances, UndecidableInstances,
              TypeOperators #-}
 -- | Extensible options. They are used for provider-specific settings,
 -- ingredient-specific settings and core settings (such as the test name pattern).
@@ -29,9 +29,12 @@
 import Data.Typeable
 import Data.Monoid
 import Data.Foldable
-import Prelude  -- Silence FTP import warnings
-
+import Prelude hiding (mod) -- Silence FTP import warnings
 import Options.Applicative
+#if MIN_VERSION_base(4,9,0)
+import Data.Semigroup (Semigroup)
+import qualified Data.Semigroup (Semigroup((<>)))
+#endif
 
 -- | An option is a data type that inhabits the `IsOption` type class.
 class Typeable v => IsOption v where
@@ -82,6 +85,10 @@
   mempty = OptionSet mempty
   OptionSet a `mappend` OptionSet b =
     OptionSet $ Map.unionWith (flip const) a b
+#if MIN_VERSION_base(4,9,0)
+instance Semigroup OptionSet where
+  (<>) = mappend
+#endif
 
 -- | Set the option value
 setOption :: IsOption v => v -> OptionSet -> OptionSet
diff --git a/Test/Tasty/Options/Core.hs b/Test/Tasty/Options/Core.hs
--- a/Test/Tasty/Options/Core.hs
+++ b/Test/Tasty/Options/Core.hs
@@ -1,5 +1,5 @@
 -- | Core options, i.e. the options used by tasty itself
-{-# LANGUAGE DeriveDataTypeable, GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE CPP, DeriveDataTypeable, GeneralizedNewtypeDeriving #-}
 {-# OPTIONS_GHC -fno-warn-type-defaults #-} -- for (^)
 module Test.Tasty.Options.Core
   ( NumThreads(..)
@@ -12,12 +12,13 @@
 import Control.Monad (mfilter)
 import Data.Proxy
 import Data.Typeable
+#if !MIN_VERSION_base(4,8,0)
 import Data.Tagged
-import Data.Fixed
 import Data.Monoid
-import Options.Applicative
+#endif
+import Data.Fixed
+import Options.Applicative hiding (str)
 import GHC.Conc
-import Prelude  -- Silence FTP import warnings
 
 import Test.Tasty.Options
 import Test.Tasty.Patterns
diff --git a/Test/Tasty/Parallel.hs b/Test/Tasty/Parallel.hs
--- a/Test/Tasty/Parallel.hs
+++ b/Test/Tasty/Parallel.hs
@@ -125,7 +125,7 @@
           -- an exception strikes before we 'release'. Everything will be
           -- killed, so why bother.
           return $ do
-            pid <- forkCarefully (do a; release)
+            pid <- forkCarefully (do a :: IO (); release)
             labelThread pid "tasty_test_thread"
             cont
 
diff --git a/Test/Tasty/Patterns.hs b/Test/Tasty/Patterns.hs
--- a/Test/Tasty/Patterns.hs
+++ b/Test/Tasty/Patterns.hs
@@ -28,7 +28,7 @@
 --
 -- (Most of the code borrowed from the test-framework)
 
-{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE CPP, DeriveDataTypeable #-}
 
 module Test.Tasty.Patterns
   ( TestPattern
@@ -44,10 +44,12 @@
 
 import Data.List
 import Data.Typeable
+#if !MIN_VERSION_base(4,8,0)
 import Data.Tagged
+import Data.Monoid
+#endif
 
 import Options.Applicative
-import Data.Monoid
 
 data Token = SlashToken
            | WildcardToken
diff --git a/Test/Tasty/Run.hs b/Test/Tasty/Run.hs
--- a/Test/Tasty/Run.hs
+++ b/Test/Tasty/Run.hs
@@ -196,7 +196,7 @@
 -- | Turn a test tree into a list of actions to run tests coupled with
 -- variables to watch them
 createTestActions :: OptionSet -> TestTree -> IO ([(IO (), TVar Status)], [ResourceVar])
-createTestActions opts tree = do
+createTestActions opts0 tree = do
   let
     traversal ::
       Traversal (WriterT ([(InitFinPair -> IO (), TVar Status)], [ResourceVar]) IO)
@@ -206,7 +206,7 @@
           { foldSingle = runSingleTest
           , foldResource = addInitAndRelease
           }
-        opts tree
+        opts0 tree
   (tests, rvars) <- unwrap traversal
   let tests' = map (first ($ (Seq.empty, Seq.empty))) tests
   return (tests', rvars)
@@ -261,17 +261,17 @@
     -- all resource initializers and finalizers, which is why it is more
     -- accurate than what could be measured from inside the first callback.
   -> IO a
-launchTestTree opts tree k = do
+launchTestTree opts tree k0 = do
   (testActions, rvars) <- createTestActions opts tree
   let NumThreads numTheads = lookupOption opts
-  (t,k) <- timed $ do
+  (t,k1) <- timed $ do
      abortTests <- runInParallel numTheads (fst <$> testActions)
      (do let smap = IntMap.fromList $ zip [0..] (snd <$> testActions)
-         k smap)
+         k0 smap)
       `finally` do
          abortTests
          waitForResources rvars
-  k t
+  k1 t
   where
     alive :: Resource r -> Bool
     alive r = case r of
@@ -304,5 +304,10 @@
 getTime :: IO Time
 getTime = do
   t <- Clock.getTime Clock.Monotonic
-  let ns = realToFrac $ Clock.timeSpecAsNanoSecs t
+  let ns = realToFrac $
+#if MIN_VERSION_clock(0,7,1)
+        Clock.toNanoSecs t
+#else
+        Clock.timeSpecAsNanoSecs t
+#endif
   return $ ns / 10 ^ (9 :: Int)
diff --git a/Test/Tasty/Runners/Reducers.hs b/Test/Tasty/Runners/Reducers.hs
--- a/Test/Tasty/Runners/Reducers.hs
+++ b/Test/Tasty/Runners/Reducers.hs
@@ -44,12 +44,20 @@
 import Data.Monoid
 import Control.Applicative
 import Prelude  -- Silence AMP import warnings
+#if MIN_VERSION_base(4,9,0)
+import Data.Semigroup (Semigroup)
+import qualified Data.Semigroup (Semigroup((<>)))
+#endif
 
 -- | Monoid generated by '*>'
 newtype Traversal f = Traversal { getTraversal :: f () }
 instance Applicative f => Monoid (Traversal f) where
   mempty = Traversal $ pure ()
   Traversal f1 `mappend` Traversal f2 = Traversal $ f1 *> f2
+#if MIN_VERSION_base(4,9,0)
+instance Applicative f => Semigroup (Traversal f) where
+  (<>) = mappend
+#endif
 
 -- | Monoid generated by @'liftA2' ('<>')@
 newtype Ap f a = Ap { getApp :: f a }
@@ -57,3 +65,7 @@
 instance (Applicative f, Monoid a) => Monoid (Ap f a) where
   mempty = pure mempty
   mappend = liftA2 mappend
+#if MIN_VERSION_base(4,9,0)
+instance (Applicative f, Monoid a) => Semigroup (Ap f a) where
+  (<>) = mappend
+#endif
diff --git a/Test/Tasty/Runners/Utils.hs b/Test/Tasty/Runners/Utils.hs
--- a/Test/Tasty/Runners/Utils.hs
+++ b/Test/Tasty/Runners/Utils.hs
@@ -15,7 +15,7 @@
 --
 -- See e.g. <https://github.com/feuerbach/tasty/issues/25>
 formatMessage :: String -> IO String
-formatMessage msg = go 3 msg
+formatMessage = go 3
   where
     -- to avoid infinite recursion, we introduce the recursion limit
     go :: Int -> String -> IO String
diff --git a/tasty.cabal b/tasty.cabal
--- a/tasty.cabal
+++ b/tasty.cabal
@@ -2,7 +2,7 @@
 --  see http://haskell.org/cabal/users-guide/
 
 name:                tasty
-version:             0.12
+version:             0.12.0.1
 synopsis:            Modern and extensible testing framework
 description:         Tasty is a modern testing framework for Haskell.
                      It lets you combine your unit tests, golden
@@ -70,4 +70,5 @@
 
   -- hs-source-dirs:      
   default-language:    Haskell2010
-  ghc-options: -Wall -fno-warn-unused-do-bind -fno-warn-name-shadowing
+  default-extensions:  CPP
+  ghc-options: -Wall