diff --git a/html/semantics/forms/the-select-element/select-child-button-and-datalist-invalidation.tentative.html b/html/semantics/forms/the-select-element/select-child-button-and-datalist-invalidation.tentative.html
new file mode 100644
index 000000000000000..f71c1e52fc612ba
--- /dev/null
+++ b/html/semantics/forms/the-select-element/select-child-button-and-datalist-invalidation.tentative.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html class=reftest-wait>
+<link rel=author href="mailto:jarhar@chromium.org">
+<link rel=help href="https://github.com/whatwg/html/issues/9799">
+<link rel=match href="select-child-button-and-datalist-ref.html">
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+
+<select>
+  <button type=popover>button</button>
+  <datalist>
+    <option>one</option>
+    <option>two</option>
+  </datalist>
+</select>
+
+<script>
+requestAnimationFrame(() => {
+  document.querySelector('select').style = 'appearance:bikeshed';
+  document.querySelector('button').click();
+  document.documentElement.classList.remove('reftest-wait');
+});
+</script>
diff --git a/html/semantics/forms/the-select-element/select-child-button-and-datalist.tentative.html b/html/semantics/forms/the-select-element/select-child-button-and-datalist.tentative.html
index b74957feed89b7c..54785ace95150ef 100644
--- a/html/semantics/forms/the-select-element/select-child-button-and-datalist.tentative.html
+++ b/html/semantics/forms/the-select-element/select-child-button-and-datalist.tentative.html
@@ -5,7 +5,7 @@
 <script src="/resources/testdriver.js"></script>
 <script src="/resources/testdriver-vendor.js"></script>
 
-<select>
+<select style="appearance:bikeshed">
   <button type=popover>button</button>
   <datalist>
     <option>one</option>
