diff --git a/eio_windows.opam b/eio_windows.opam
old mode 100755
new mode 100644
index 7ad94c870..b1b6b795c
--- a/eio_windows.opam
+++ b/eio_windows.opam
@@ -30,3 +30,4 @@ build: [
   ]
 ]
 dev-repo: "git+https://github.com/ocaml-multicore/eio.git"
+available: [os-family = "windows"]
diff --git a/eio_windows.opam.template b/eio_windows.opam.template
new file mode 100644
index 000000000..e8e4096c8
--- /dev/null
+++ b/eio_windows.opam.template
@@ -0,0 +1 @@
+available: [os-family = "windows"]