diff --git a/testing/web-platform/tests/html/rendering/pixel-length-attributes.html b/testing/web-platform/tests/html/rendering/pixel-length-attributes.html
index e2cb8269a7f2..888e6d0a3ff7 100644
--- a/testing/web-platform/tests/html/rendering/pixel-length-attributes.html
+++ b/testing/web-platform/tests/html/rendering/pixel-length-attributes.html
@@ -1,5 +1,7 @@
 <!doctype html>
 <meta charset=utf-8>
+<!-- Creating iframes is slow in browsers -->
+<meta name=timeout content=long>
 <title>Test handling of attributes that map to pixel length properties</title>
 <link rel="help"
       href="https://html.spec.whatwg.org/multipage/rendering.html#maps-to-the-pixel-length-property">
