fix: remove value and writable properties from headers descriptor (#12552)

2 files changed, 15 insertions, 3 deletions

diff --git a/.changeset/tame-hats-fold.md b/.changeset/tame-hats-fold.md
new file mode 100644
index 000000000..e369aa8d4
--- /dev/null
+++ b/.changeset/tame-hats-fold.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixed an issue where modifying the `Request.headers` prototype during prerendering caused a build error. Removed conflicting value and writable properties from the `headers` descriptor to prevent `Invalid property descriptor` errors.
diff --git a/packages/astro/src/core/request.ts b/packages/astro/src/core/request.ts
index 3ace80ba8..624bee879 100644
--- a/packages/astro/src/core/request.ts
+++ b/packages/astro/src/core/request.ts
@@ -70,9 +70,13 @@ export function createRequest({
 	});
 
 	if (isPrerendered) {
-		// Warn when accessing headers in prerendered pages
-		const _headers = request.headers;
-		const headersDesc = Object.getOwnPropertyDescriptor(request, 'headers') || {};
+		// Warn when accessing headers in SSG mode
+		let _headers = request.headers;
+
+		// We need to remove descriptor's value and writable properties because we're adding getters and setters.
+		const { value, writable, ...headersDesc } =
+			Object.getOwnPropertyDescriptor(request, 'headers') || {};
+
 		Object.defineProperty(request, 'headers', {
 			...headersDesc,
 			get() {
@@ -82,6 +86,9 @@ export function createRequest({
 				);
 				return _headers;
 			},
+			set(newHeaders: Headers) {
+				_headers = newHeaders;
+			},
 		});
 	} else if (clientAddress) {
 		// clientAddress is stored to be read by RenderContext, only if the request is for a page that will be on-demand rendered