diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 0.3.1 [2018.01.18]
+* Fix the build on GHC 8.4.
+
 ## 0.3
 * `Observable` instances can be derived for `Generic` instances using
   `DefaultSignatures` ([MaartenFaddegon](https://github.com/ku-fpg/hood/pull/1))
diff --git a/Debug/Hood/Observe.hs b/Debug/Hood/Observe.hs
--- a/Debug/Hood/Observe.hs
+++ b/Debug/Hood/Observe.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE DefaultSignatures #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
@@ -61,6 +62,7 @@
 
   , debugO         -- IO a -> IO [CDS]
   , CDS(..)
+  , CDSSet
   ) where
 
 {-
@@ -97,7 +99,11 @@
 -}
 import Data.Dynamic ( Dynamic )
 
-import Prelude
+import Prelude hiding (
+#if MIN_VERSION_base(4,11,0)
+                        (<>)
+#endif
+                      )
 
 infixl 9 <<
 
@@ -162,7 +168,7 @@
        ; let cdss2 = simplifyCDSSet cdss1
        ; let output1 = cdssToOutput cdss2
        ; let output2 = commonOutput output1
-       ; let ptyout  = pretty 80 (foldr (<>) nil (map renderTop output2))
+       ; let ptyout  = pretty 80 $ foldr ((<>) . renderTop) nil output2
        ; hPutStrLn stderr ""
        ; hPutStrLn stderr ptyout
        }
@@ -308,7 +314,7 @@
          - This used used to group several observer instances together.
          -}
         observers :: String -> (Observer -> a) -> a
-        observers label arg = defaultObservers label arg
+        observers = defaultObservers
 
 class GObservable f where
         gdmobserver :: f a -> Parent -> f a
@@ -354,7 +360,7 @@
 
 -- Products: encode multiple arguments to constructors
 instance (GObservable a, GObservable b) => GObservable (a :*: b) where
-        gdmobserver (a :*: b) cxt = (gdmobserver a cxt) :*: (gdmobserver b cxt)
+        gdmobserver (a :*: b) cxt = gdmobserver a cxt :*: gdmobserver b cxt
         gdmObserveChildren (a :*: b) = do a'  <- gdmObserveChildren a
                                           b'  <- gdmObserveChildren b
                                           return (a' :*: b')
@@ -368,14 +374,14 @@
 
 gthunk :: (GObservable f) => f a -> ObserverM (f a)
 gthunk a = ObserverM $ \ parent port ->
-                ( gdmobserver_ a (Parent
+                ( gdmobserver_ a Parent
                                 { observeParent = parent
                                 , observePort   = port
-                                })
+                                }
                 , port+1 )
 
 gdmobserver_ :: (GObservable f) => f a -> Parent -> f a
-gdmobserver_ a context = gsendEnterPacket a context
+gdmobserver_ = gsendEnterPacket
 
 gsendEnterPacket :: (GObservable f) => f a -> Parent -> f a
 gsendEnterPacket r context = unsafeWithUniq $ \ node ->
@@ -395,16 +401,16 @@
                = unsafeWithUniq $ \ subnode ->
                  do { sendEvent subnode (Parent node 0)
                                         (Observe sublabel)
-                    ; return (observer_ a (Parent
+                    ; return (observer_ a Parent
                         { observeParent = subnode
                         , observePort   = 0
-                        }))
+                        })
                     }
         ; return (observer_ (fn (O observe'))
-                       (Parent
+                       Parent
                         { observeParent = node
                         , observePort   = 0
-                        }))
+                        })
         }
 defaultFnObservers :: (Observable a, Observable b)
                       => String -> (Observer -> a -> b) -> a -> b
@@ -414,16 +420,16 @@
                = unsafeWithUniq $ \ subnode ->
                  do { sendEvent subnode (Parent node 0)
                                         (Observe sublabel)
-                    ; return (observer_ a (Parent
+                    ; return (observer_ a Parent
                         { observeParent = subnode
                         , observePort   = 0
-                        }))
+                        })
                     }
         ; return (observer_ (fn (O observe'))
-                       (Parent
+                       Parent
                         { observeParent = node
                         , observePort   = 0
-                        }) arg)
+                        } arg)
         }
 
 {-
@@ -455,10 +461,10 @@
 
 thunk :: (Observable a) => a -> ObserverM a
 thunk a = ObserverM $ \ parent port ->
-                ( observer_ a (Parent
+                ( observer_ a Parent
                                 { observeParent = parent
                                 , observePort   = port
-                                })
+                                }
                 , port+1 )
 
 (<<) :: (Observable a) => ObserverM (a -> b) -> a -> ObserverM b
@@ -488,7 +494,7 @@
 --
 {-# NOINLINE observe #-}
 observe :: (Observable a) => String -> a -> a
-observe name a = generateContext name a
+observe = generateContext
 
 {- This gets called before observer, allowing us to mark
  - we are entering a, before we do case analysis on
@@ -497,7 +503,7 @@
 
 {-# NOINLINE observer_ #-}
 observer_ :: (Observable a) => a -> Parent -> a
-observer_ a context = sendEnterPacket a context
+observer_ = sendEnterPacket
 
 data Parent = Parent
         { observeParent :: !Int -- my parent
@@ -510,17 +516,19 @@
 
 unsafeWithUniq :: (Int -> IO a) -> a
 unsafeWithUniq fn
-  = unsafePerformIO $ do { node <- getUniq
-                         ; fn node
+  = unsafePerformIO $ do { node <- readUniq
+                         ; r <- fn node
+                         ; incrementUniq node
+                         ; return r
                          }
 
 generateContext :: (Observable a) => String -> a -> a
 generateContext label orig = unsafeWithUniq $ \ node ->
      do { sendEvent node (Parent 0 0) (Observe label)
-        ; return (observer_ orig (Parent
+        ; return (observer_ orig Parent
                         { observeParent = node
                         , observePort   = 0
-                        })
+                        }
                   )
         }
 
@@ -595,6 +603,7 @@
            }
 
 -- local
+{-# NOINLINE events #-}
 events :: IORef [Event]
 events = unsafePerformIO $ newIORef badEvents
 
@@ -620,17 +629,11 @@
 initUniq :: IO ()
 initUniq = writeIORef uniq 1
 
-getUniq :: IO Int
-getUniq
-    = do { takeMVar uniqSem
-         ; n <- readIORef uniq
-         ; writeIORef uniq $! (n + 1)
-         ; putMVar uniqSem ()
-         ; return n
-         }
+incrementUniq :: Int -> IO ()
+incrementUniq n = writeIORef uniq $! (n + 1)
 
-peepUniq :: IO Int
-peepUniq = readIORef uniq
+readUniq :: IO Int
+readUniq = readIORef uniq
 
 -- locals
 {-# NOINLINE uniq #-}
@@ -682,7 +685,7 @@
 eventsToCDS :: [Event] -> CDSSet
 eventsToCDS pairs = getChild 0 0
    where
-     res i = (!) out_arr i
+     res = (!) out_arr
 
      bnds = (0, length pairs)
 
@@ -716,7 +719,7 @@
 
 render  :: Int -> Bool -> CDS -> Doc
 render prec par (CDSCons _ ":" [cds1,cds2]) =
-        if (par && not needParen)
+        if par && not needParen
         then doc -- dont use paren (..) because we dont want a grp here!
         else paren needParen doc
    where
@@ -780,7 +783,7 @@
 findFn' other rest = ([],[other]) : rest
 
 renderTops []   = nil
-renderTops tops = line <> foldr (<>) nil (map renderTop tops)
+renderTops tops = line <> foldr ((<>) . renderTop ) nil tops
 
 renderTop :: Output -> Doc
 renderTop (OutLabel str set extras) =
diff --git a/hood.cabal b/hood.cabal
--- a/hood.cabal
+++ b/hood.cabal
@@ -1,5 +1,5 @@
 Name:                hood
-Version:             0.3
+Version:             0.3.1
 Synopsis:            Debugging by observing in place
 Description:         Hood debugger, based on the idea of observing functions and structures as they are evaluated.
 Category:            Debug, Trace
@@ -8,7 +8,7 @@
 Author:              Andy Gill
 Maintainer:          Andy Gill <andygill@ku.edu>
 Copyright:           (c) 2000 Andy Gill, (c) 2010-2015 University of Kansas, (c) 2013-2015 Maarten Faddegon
-Homepage:            http://www.ittc.ku.edu/csdl/fpg/Hood
+Homepage:            http://ku-fpg.github.io/software/hood
 bug-reports:         https://github.com/ku-fpg/hood/issues
 Stability:           alpha
 build-type:          Simple
@@ -17,12 +17,21 @@
                    , GHC == 7.6.3
                    , GHC == 7.8.4
                    , GHC == 7.10.3
+                   , GHC == 8.0.2
+                   , GHC == 8.2.2
+                   , GHC == 8.4.1
 extra-source-files:  CHANGELOG.md, README.md
 
 Library
   Build-Depends: base >= 4.5 && < 5, array, FPretty, ghc-prim
   Exposed-modules:
       Debug.Hood.Observe
+
+Test-Suite hood-test
+  Type:                exitcode-stdio-1.0
+  Hs-Source-Dirs:      test
+  Main-Is:             test.hs
+  Build-Depends:       base, ghc-prim, hood
 
 source-repository head
     type:     git
diff --git a/test/test.hs b/test/test.hs
new file mode 100644
--- /dev/null
+++ b/test/test.hs
@@ -0,0 +1,26 @@
+#!/usr/bin/env stack
+{-# LANGUAGE DeriveGeneric #-}
+-- stack --resolver lts-8.4 runghc --package hood
+-- Minimum program to reproduce https://github.com/ku-fpg/hood/issues/5
+
+import           Debug.Hood.Observe
+import           GHC.Generics
+
+
+data Hoge =
+  Hoge
+    { hoge1 :: Int
+    , hoge2 :: String
+    } deriving Generic
+
+instance Observable Hoge
+
+
+main :: IO ()
+main = runO $ print $ f undefined
+
+
+f :: Hoge -> Bool
+f = observe "f" f'
+f' :: Hoge -> Bool
+f' h@(Hoge _h1 _h2) = error "ERROR"