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diff --git a/testing/web-platform/tests/layout-instability/clip-negative-bottom-margin.html b/testing/web-platform/tests/layout-instability/clip-negative-bottom-margin.html
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+++ b/testing/web-platform/tests/layout-instability/clip-negative-bottom-margin.html
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+<!DOCTYPE html>
+<title>Layout Instability: clip with negative bottom margin</title>
+<link rel="help" href="https://wicg.github.io/layout-instability/" />
+<style>
+
+#scroller { overflow: scroll; width: 200px; height: 500px; }
+#space { height: 1000px; margin-bottom: -500px; }
+#j { width: 150px; height: 150px; background: yellow; }
+
+</style>
+<div id='scroller'>
+  <div id='space'></div>
+  <div id='j'></div>
+</div>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/util.js"></script>
+<script>
+
+promise_test(async () => {
+  const watcher = new ScoreWatcher;
+
+  // Wait for the initial render to complete.
+  await waitForAnimationFrames(2);
+
+  // Increase j's top margin by 100px. Since j is fully clipped by the scroller,
+  // this should not generate a shift.
+  document.querySelector("#j").style.marginTop = "100px";
+
+  await waitForAnimationFrames(3);
+  assert_equals(watcher.score, 0);
+}, "Clip with negative bottom margin.");
+
+</script>
+
+