diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index a8d4a49..6cda41d 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -15,6 +15,9 @@ jobs:
       matrix:
         os:
           - ubuntu-latest
+          - macos-latest
+          - windows-latest
+
         ocaml-compiler:
           - "4.14"
           - "5.1"
@@ -38,7 +41,7 @@ jobs:
 
       - run: opam install . --deps-only --with-test
 
-      - run: opam exec -- dune build -p mlx,ocamlmerlin-mlx
+      - run: opam exec -- dune build -p mlx
 
         # TODO: pass --with-dev-setup to opam instead? (requires opam 2.2, I think)
       - run: opam install menhir.20201216 menhirLib.20201216 menhirSdk.20201216 ocamlformat
diff --git a/mlx/pp.ml b/mlx/pp.ml
index 81fc498..5573e5c 100644
--- a/mlx/pp.ml
+++ b/mlx/pp.ml
@@ -32,6 +32,7 @@ let () =
       if !print_ml then Format.printf "%a@." Pprintast.structure str
       else
         let oc = stdout in
+        Out_channel.set_binary_mode oc true;
         output_string oc
           Ppxlib_ast.Compiler_version.Ast.Config.ast_impl_magic_number;
         output_value oc fname;