diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -6,6 +6,10 @@
 and this project adheres to the
 [Haskell Package Versioning Policy](https://pvp.haskell.org/).
 
+## v0.6.6 — 2023-10-02
+
+- Fix builds on Windows (and macOS) (see [#121](https://github.com/rzk-lang/rzk/pull/121))
+
 ## v0.6.5 — 2023-10-01
 
 This version contains mostly intrastructure improvements:
diff --git a/Setup.hs b/Setup.hs
--- a/Setup.hs
+++ b/Setup.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 -- Source: https://github.com/haskell/cabal/issues/6726#issuecomment-918663262
 
 -- | Custom Setup that runs bnfc to generate the language sub-libraries
@@ -18,7 +19,9 @@
 main = defaultMainWithHooks $ simpleUserHooks
   { hookedPrograms = [ bnfcProgram ]
   , postConf       = \args flags packageDesc localBuildInfo -> do
+#ifndef mingw32_HOST_OS
       _ <- system "bnfc -d -p Language.Rzk --generic --functor -o src/ grammar/Syntax.cf"
+#endif
       postConf simpleUserHooks args flags packageDesc localBuildInfo
   }
 
diff --git a/rzk.cabal b/rzk.cabal
--- a/rzk.cabal
+++ b/rzk.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           rzk
-version:        0.6.5
+version:        0.6.6
 synopsis:       An experimental proof assistant for synthetic ∞-categories
 description:    Please see the README on GitHub at <https://github.com/rzk-lang/rzk#readme>
 category:       Dependent Types
@@ -56,7 +56,7 @@
       Paths_rzk
   hs-source-dirs:
       src
-  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -optP-Wno-nonportable-include-path
   build-tools:
       alex >=3.2.4
     , happy >=1.19.9
@@ -99,7 +99,7 @@
       Paths_rzk
   hs-source-dirs:
       app
-  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -optP-Wno-nonportable-include-path -threaded -rtsopts -with-rtsopts=-N
   build-tools:
       alex >=3.2.4
     , happy >=1.19.9
@@ -128,7 +128,7 @@
   main-is: doctests.hs
   hs-source-dirs:
       test
-  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -optP-Wno-nonportable-include-path
   build-tools:
       alex >=3.2.4
     , happy >=1.19.9
@@ -157,7 +157,7 @@
       Paths_rzk
   hs-source-dirs:
       test
-  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -optP-Wno-nonportable-include-path -threaded -rtsopts -with-rtsopts=-N
   build-tools:
       alex >=3.2.4
     , happy >=1.19.9