diff --git a/server/src/lib/pdf.ts b/server/src/lib/pdf.ts
index 49bf2d1..aaec709 100644
--- a/server/src/lib/pdf.ts
+++ b/server/src/lib/pdf.ts
@@ -13,13 +13,15 @@ export async function renderPdf(html: string) {
     const page = await browser.newPage();
     await page.setContent(html, { waitUntil: "networkidle0" });
 
-    return await page.pdf({
+    const pdf = await page.pdf({
       format: "A4",
       printBackground: true,
       preferCSSPageSize: true,
     });
+
+    // Normalize Puppeteer's Uint8Array output to a Node Buffer so Express sends a valid PDF payload.
+    return Buffer.from(pdf);
   } finally {
     await browser.close();
   }
 }
-