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diff --git a/testing/web-platform/tests/css/css-contain/container-queries/fragmented-container-001.html b/testing/web-platform/tests/css/css-contain/container-queries/fragmented-container-001.html
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+++ b/testing/web-platform/tests/css/css-contain/container-queries/fragmented-container-001.html
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+<!doctype html>
+<title>CSS Container Queries Test: Query fragmented inline-size container</title>
+<link rel="help" href="https://drafts.csswg.org/css-contain-3/#size-container">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="support/cq-testcommon.js"></script>
+<style>
+  #multicol {
+    width: 400px;
+    column-count: 2;
+    column-fill: auto;
+    column-gap: 0;
+    height: 100px;
+  }
+  #float {
+    float: left;
+    width: 100px;
+    height: 50px;
+  }
+  #container {
+    container-type: inline-size;
+    display: flow-root;
+    height: 200px;
+  }
+  #first-child {
+    break-after: column;
+  }
+  @container (width = 100px) {
+    #first-child { color: green; }
+    #second-child { color: green; }
+  }
+</style>
+<div id="multicol">
+  <div id="float"></div>
+  <div id="container">
+    <div id="first-child"></div>
+    <div id="second-child"></div>
+  </div>
+</div>
+<script>
+  setup(() => assert_implements_container_queries());
+
+  test(() => {
+    const green = "rgb(0, 128, 0)";
+    assert_equals(getComputedStyle(document.querySelector("#first-child")).color, green);
+    assert_equals(getComputedStyle(document.querySelector("#second-child")).color, green);
+  }, "Children of fragmented inline-size container should match inline-size of first fragment");
+</script>