diff --git a/x86/macaw-x86.cabal b/x86/macaw-x86.cabal
index a4904a7c..186f0993 100644
--- a/x86/macaw-x86.cabal
+++ b/x86/macaw-x86.cabal
@@ -46,6 +46,8 @@ library
   ghc-options: -Wall
   ghc-options: -fno-warn-unticked-promoted-constructors
   ghc-prof-options: -O2 -fprof-auto-top
+  if impl(ghc >= 8.6)
+     default-extensions: NoStarIsType
 
 test-suite macaw-x86-tests
   type: exitcode-stdio-1.0
diff --git a/x86/src/Data/Macaw/X86/ArchTypes.hs b/x86/src/Data/Macaw/X86/ArchTypes.hs
index 8889687e..81b00367 100644
--- a/x86/src/Data/Macaw/X86/ArchTypes.hs
+++ b/x86/src/Data/Macaw/X86/ArchTypes.hs
@@ -38,6 +38,7 @@ module Data.Macaw.X86.ArchTypes
   ) where
 
 import           Data.Bits
+import qualified Data.Kind as Kind
 import           Data.Word(Word8)
 import           Data.Macaw.CFG
 import           Data.Macaw.CFG.Rewriter
@@ -877,7 +878,7 @@ x86PrimFnHasSideEffects f =
 -- X86Stmt
 
 -- | An X86 specific statement.
-data X86Stmt (v :: Type -> *) where
+data X86Stmt (v :: Type -> Kind.Type) where
   WriteLoc :: !(X86PrimLoc tp) -> !(v tp) -> X86Stmt v
 
   -- | Store the X87 control register in the given address.
diff --git a/x86/src/Data/Macaw/X86/Generator.hs b/x86/src/Data/Macaw/X86/Generator.hs
index 80337ac5..109f3a65 100644
--- a/x86/src/Data/Macaw/X86/Generator.hs
+++ b/x86/src/Data/Macaw/X86/Generator.hs
@@ -61,6 +61,7 @@ module Data.Macaw.X86.Generator
 import           Control.Lens
 import           Control.Monad.Cont
 import           Control.Monad.Except
+import           Control.Monad.Fail
 import           Control.Monad.Reader
 import           Control.Monad.ST
 import           Control.Monad.State.Strict
@@ -267,6 +268,8 @@ instance Monad (X86Generator st_s ids) where
   return v = seq v $ X86G $ return v
   (X86G m) >>= h = X86G $ m >>= \v -> seq v (unX86G (h v))
   X86G m >> X86G n = X86G $ m >> n
+
+instance MonadFail (X86Generator st_s ids) where
   fail msg = seq t $ X86G $ ContT $ \_ -> throwError t
     where t = Text.pack msg