diff --git a/testing/web-platform/tests/html/rendering/widgets/field-sizing-textarea.html b/testing/web-platform/tests/html/rendering/widgets/field-sizing-textarea.html
index f8d90dc659b11..114d60c72d023 100644
--- a/testing/web-platform/tests/html/rendering/widgets/field-sizing-textarea.html
+++ b/testing/web-platform/tests/html/rendering/widgets/field-sizing-textarea.html
@@ -3,6 +3,10 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <style>
+textarea {
+  font-family: monospace;
+}
+
 .disable-default {
   field-sizing: content;
 }