diff --git a/packages/astro-early-hints/src/middleware/index.ts b/packages/astro-early-hints/src/middleware/index.ts
index 24593eb..04bc436 100644
--- a/packages/astro-early-hints/src/middleware/index.ts
+++ b/packages/astro-early-hints/src/middleware/index.ts
@@ -10,19 +10,23 @@ export const onRequest = defineMiddleware(async (_, next) => {
 	const root = parse(await response.text());
 	const head = root.querySelector("head")!;
 
-	root.querySelectorAll('link[rel="stylesheet"]').map((style) => {
-		head.insertAdjacentHTML(
-			"afterbegin",
-			`<link rel="preload" as="style" href="${style.getAttribute("href")}">`,
-		);
-	});
+	root.querySelectorAll('link[rel="stylesheet"]')
+		.filter((style) => style.hasAttribute("href") && style.getAttribute("href"))
+		.map((style) => {
+			head.insertAdjacentHTML(
+				"afterbegin",
+				`<link rel="preload" as="style" href="${style.getAttribute("href")}">`,
+			);
+		});
 
-	root.querySelectorAll('script[type="module"]').map((script) => {
-		head.insertAdjacentHTML(
-			"afterbegin",
-			`<link rel="modulepreload" href="${script.getAttribute("src")}">`,
-		);
-	});
+	root.querySelectorAll('script[type="module"]')
+		.filter((script) => script.hasAttribute("src") && script.getAttribute("src"))
+		.map((script) => {
+			head.insertAdjacentHTML(
+				"afterbegin",
+				`<link rel="modulepreload" href="${script.getAttribute("src")}">`,
+			);
+		});
 
 	return new Response(root.toString(), response);
 });