diff --git a/jvm.cabal b/jvm.cabal
--- a/jvm.cabal
+++ b/jvm.cabal
@@ -1,5 +1,5 @@
 name:                jvm
-version:             0.1
+version:             0.1.1
 synopsis:            Call JVM methods from Haskell.
 description:         Please see README.md.
 homepage:            http://github.com/tweag/inline-java/tree/master/jvm#readme
diff --git a/src/Language/Java.hs b/src/Language/Java.hs
--- a/src/Language/Java.hs
+++ b/src/Language/Java.hs
@@ -29,6 +29,7 @@
 -- __NOTE:__ To use any function in this module, you'll need an initialized JVM in the
 -- current process, using 'withJVM' or otherwise.
 
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DefaultSignatures #-}
 {-# LANGUAGE FlexibleContexts #-}
@@ -61,7 +62,7 @@
 
 import Control.Distributed.Closure
 import Control.Distributed.Closure.TH
-import Control.Monad ((<=<), forM, forM_)
+import Control.Monad
 import Data.Char (chr, ord)
 import qualified Data.Coerce as Coerce
 import Data.Int
@@ -73,11 +74,13 @@
 import Data.String (fromString)
 import qualified Data.Text.Foreign as Text
 import Data.Text (Text)
+#if ! __GLASGOW_HASKELL__ == 800
 import qualified Data.Vector.Storable as Vector
 import Data.Vector.Storable (Vector)
 import qualified Data.Vector.Storable.Mutable as MVector
 import Data.Vector.Storable.Mutable (IOVector)
 import Foreign (FunPtr, Ptr, Storable, newForeignPtr, withForeignPtr)
+#endif
 import Foreign.C (CChar)
 import Foreign.JNI
 import Foreign.JNI.Types
@@ -150,13 +153,13 @@
 
 -- | Get the Java class of an object or anything 'Coercible' to one.
 classOf
-  :: ( Coerce.Coercible a (J ('Class sym))
-     , Coercible a ('Class sym)
+  :: ( Coercible a ('Class sym)
      , KnownSymbol sym
      )
   => a
   -> Sing sym
-classOf _ = sing
+-- Silence redundant constraint warning.
+classOf x = coerce x `seq` sing
 
 -- | Creates a new instance of the class whose name is resolved from the return
 -- type. For instance,
@@ -169,7 +172,6 @@
   :: forall a sym.
      ( Coerce.Coercible a (J ('Class sym))
      , Coercible a ('Class sym)
-     , KnownSymbol sym
      )
   => [JValue]
   -> IO a
@@ -286,6 +288,7 @@
 class (Interp (Uncurry a) ~ ty, SingI ty) => Reflect a ty where
   reflect :: a -> IO (J ty)
 
+#if ! __GLASGOW_HASKELL__ == 800
 foreign import ccall "wrapper" wrapFinalizer
   :: (Ptr a -> IO ())
   -> IO (FunPtr (Ptr a -> IO ()))
@@ -314,6 +317,7 @@
     jobj <- newfun (fromIntegral n)
     withForeignPtr fptr $ fill jobj 0 (fromIntegral n)
     return jobj
+#endif
 
 withStatic [d|
   type instance Interp (J ty) = ty
@@ -442,6 +446,9 @@
         Text.useAsPtr x $ \ptr len ->
           newString ptr (fromIntegral len)
 
+-- Instances can't be compiled on GHC 8.0.1 due to
+-- https://ghc.haskell.org/trac/ghc/ticket/12082.
+#if ! __GLASGOW_HASKELL__ == 800
   type instance Interp (IOVector Int32) = 'Array ('Prim "int")
 
   instance Reify (IOVector Int32) ('Array ('Prim "int")) where
@@ -457,6 +464,7 @@
 
   instance Reflect (Vector Int32) ('Array ('Prim "int")) where
     reflect = reflect <=< Vector.thaw
+#endif
 
   type instance Interp [a] = 'Array (Interp (Uncurry a))