diff --git a/src/XMonad/Layout.hs b/src/XMonad/Layout.hs
index 8eff488..9c01a69 100644
--- a/src/XMonad/Layout.hs
+++ b/src/XMonad/Layout.hs
@@ -137,7 +137,7 @@ data ChangeLayout = FirstLayout | NextLayout deriving (Eq, Show, Typeable)
 instance Message ChangeLayout
 
 -- | The layout choice combinator
-(|||) :: (LayoutClass l a, LayoutClass r a) => l a -> r a -> Choose l r a
+(|||) :: l a -> r a -> Choose l r a
 (|||) = Choose L
 infixr 5 |||
 
diff --git a/src/XMonad/StackSet.hs b/src/XMonad/StackSet.hs
index a7e9f6b..d117b4a 100644
--- a/src/XMonad/StackSet.hs
+++ b/src/XMonad/StackSet.hs
@@ -477,12 +477,12 @@ insertUp a s = if member a s then s else insert
 --
 --   * otherwise, delete doesn't affect the master.
 --
-delete :: (Ord a, Eq s) => a -> StackSet i l a s sd -> StackSet i l a s sd
+delete :: (Ord a) => a -> StackSet i l a s sd -> StackSet i l a s sd
 delete w = sink w . delete' w
 
 -- | Only temporarily remove the window from the stack, thereby not destroying special
 -- information saved in the 'Stackset'
-delete' :: (Eq a, Eq s) => a -> StackSet i l a s sd -> StackSet i l a s sd
+delete' :: (Eq a) => a -> StackSet i l a s sd -> StackSet i l a s sd
 delete' w s = s { current = removeFromScreen        (current s)
                 , visible = map removeFromScreen    (visible s)
                 , hidden  = map removeFromWorkspace (hidden  s) }
@@ -547,7 +547,7 @@ shift n s = maybe s (\w -> shiftWin n w s) (peek s)
 -- focused element on that workspace.
 -- The actual focused workspace doesn't change. If the window is not
 -- found in the stackSet, the original stackSet is returned.
-shiftWin :: (Ord a, Eq a, Eq s, Eq i) => i -> a -> StackSet i l a s sd -> StackSet i l a s sd
+shiftWin :: (Ord a, Eq s, Eq i) => i -> a -> StackSet i l a s sd -> StackSet i l a s sd
 shiftWin n w s = case findTag w s of
                     Just from | n `tagMember` s && n /= from -> go from s
                     _                                        -> s
diff --git a/tests/Properties/Failure.hs b/tests/Properties/Failure.hs
index fc7a359..a46d723 100644
--- a/tests/Properties/Failure.hs
+++ b/tests/Properties/Failure.hs
@@ -4,23 +4,27 @@ import XMonad.StackSet hiding (filter)
 
 import qualified Control.Exception.Extensible as C
 import System.IO.Unsafe
+import Data.List (isPrefixOf)
 
 -- ---------------------------------------------------------------------
--- testing for failure
-
--- and help out hpc
-prop_abort x = unsafePerformIO $ C.catch (abort "fail")
-                                         (\(C.SomeException e) -> return $  show e == "xmonad: StackSet: fail" )
+-- testing for failure and help out hpc
+--
+-- Since base 4.9.0.0 `error` appends a stack trace. The tests below
+-- use `isPrefixOf` to only test equality on the error message.
+--
+prop_abort :: Int -> Bool
+prop_abort _ = unsafePerformIO $ C.catch (abort "fail") check
    where
-     _ = x :: Int
+     check (C.SomeException e) =
+       return $ "xmonad: StackSet: fail" `isPrefixOf` show e
 
 -- new should fail with an abort
-prop_new_abort x = unsafePerformIO $ C.catch f
-                                         (\(C.SomeException e) -> return $ show e == "xmonad: StackSet: non-positive argument to StackSet.new" )
+prop_new_abort :: Int -> Bool
+prop_new_abort _ = unsafePerformIO $ C.catch f check
    where
      f = new undefined{-layout-} [] [] `seq` return False
-
-     _ = x :: Int
+     check (C.SomeException e) =
+       return $ "xmonad: StackSet: non-positive argument to StackSet.new" `isPrefixOf` show e
 
 -- TODO: Fix this?
 -- prop_view_should_fail = view {- with some bogus data -}
diff --git a/xmonad.cabal b/xmonad.cabal
index c5385a3..fcabdfe 100644
--- a/xmonad.cabal
+++ b/xmonad.cabal
@@ -31,7 +31,8 @@ build-type:         Simple
 tested-with:
                     GHC==7.6.3,
                     GHC==7.8.4,
-                    GHC==7.10.2
+                    GHC==7.10.3,
+                    GHC==8.0.1
 
 data-files:         man/xmonad.hs, man/xmonad.1, man/xmonad.1.html