diff --git a/.changeset/lucky-eagles-guess.md b/.changeset/lucky-eagles-guess.md
new file mode 100644
index 0000000000..3d4824b877
--- /dev/null
+++ b/.changeset/lucky-eagles-guess.md
@@ -0,0 +1,5 @@
+---
+"@inlang/paraglide-js-adapter-astro": patch
+---
+
+fix: `languageTag()` not being set properly on windows. This bug was caused by duplicate module instantiation.
diff --git a/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/integration.ts b/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/integration.ts
index 4bda251cd2..36c1e30c90 100644
--- a/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/integration.ts
+++ b/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/integration.ts
@@ -3,6 +3,7 @@ import { paraglide } from "@inlang/paraglide-js-adapter-vite"
 import path from "node:path"
 import { alias } from "./alias.js"
 import { fileURLToPath } from "node:url"
+import { normaizePath } from "./utilts.js"
 
 const __filename = fileURLToPath(import.meta.url)
 const __dirname = path.dirname(__filename)
@@ -23,6 +24,8 @@ export function integration(integrationConfig: {
 					entrypoint: middlewarePath,
 				})
 
+				const runtimePath = path.resolve(process.cwd(), integrationConfig.outdir, "runtime.js")
+
 				//Register the vite plugin
 				updateConfig({
 					vite: {
@@ -32,11 +35,10 @@ export function integration(integrationConfig: {
 								outdir: integrationConfig.outdir,
 							}),
 							alias({
-								"paraglide-js-adapter-astro:runtime": path.resolve(
-									process.cwd(),
-									integrationConfig.outdir,
-									"runtime.js"
-								),
+								//normalizing the path is very important!
+								//otherwise you get duplicate modules on windows
+								//learned that one the hard way (parjs-47)
+								"paraglide-js-adapter-astro:runtime": normaizePath(runtimePath),
 							}),
 						],
 					},
diff --git a/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/middleware.ts b/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/middleware.ts
index 48299e05ba..d75de3fec0 100644
--- a/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/middleware.ts
+++ b/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/middleware.ts
@@ -3,18 +3,19 @@ import {
 	setLanguageTag,
 	sourceLanguageTag,
 } from "paraglide-js-adapter-astro:runtime"
-import type { MiddlewareHandler } from "astro"
+import { type MiddlewareHandler } from "astro"
 
 export const onRequest: MiddlewareHandler = async ({ url, locals, currentLocale }, next) => {
 	const locale = currentLocale ?? getLangFromPath(url.pathname)
 	const dir = guessTextDirection(locale)
 
+	setLanguageTag(locale)
+
 	locals.paraglide = {
 		lang: locale,
 		dir,
 	}
 
-	setLanguageTag(locale)
 	return await next()
 }
 
diff --git a/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/utilts.ts b/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/utilts.ts
new file mode 100644
index 0000000000..b2a615854e
--- /dev/null
+++ b/inlang/source-code/paraglide/paraglide-js-adapter-astro/src/utilts.ts
@@ -0,0 +1,13 @@
+// vendored in from vite
+import path from "node:path"
+
+const windowsSlashRE = /\\/g
+function slash(p: string): string {
+	return p.replace(windowsSlashRE, "/")
+}
+
+const isWindows = typeof process !== "undefined" && process.platform === "win32"
+
+export function normaizePath(id: string) {
+	return path.posix.normalize(isWindows ? slash(id) : id)
+}