diff --git a/README.md b/README.md
index d2b7ed55a3d3b..23b98375a51f2 100644
--- a/README.md
+++ b/README.md
@@ -106,7 +106,7 @@ const puppeteer = require('puppeteer');
   await page.goto('https://news.ycombinator.com', {
     waitUntil: 'networkidle2',
   });
-  await page.pdf({ path: 'hn.pdf', format: 'A4' });
+  await page.pdf({ path: 'hn.pdf', format: 'a4' });
 
   await browser.close();
 })();