diff --git a/css/css-ui/reference/text-overflow-string-008-ref.html b/css/css-ui/reference/text-overflow-string-008-ref.html
new file mode 100644
index 00000000000000..3ad274cbb2afc3
--- /dev/null
+++ b/css/css-ui/reference/text-overflow-string-008-ref.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>CSS Basic User Interface Reference File</title>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+<style>
+  div {
+    font-family: monospace;
+    font-size: 10px;
+  }
+  span.ahem {
+    font-family: Ahem;
+    font-size: 30px;
+  }
+</style>
+<body>
+  <p>Test passes if there is a "<strong dir="ltr">ום A</strong>" after a black rectangle below.</p>
+  <div>
+    <span class="ahem">ext</span><span dir="ltr">ום A</span>
+  </div>
+</body>
+</html>
+
+    width: 130px;
\ No newline at end of file
diff --git a/css/css-ui/text-overflow-string-008.html b/css/css-ui/text-overflow-string-008.html
new file mode 100644
index 00000000000000..d2727e4bf8030a
--- /dev/null
+++ b/css/css-ui/text-overflow-string-008.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>CSS Basic User Interface Test: text-overflow with bidi string ellipsis (interaction with unicode-bidi: plaintext)</title>
+<link rel="author" title="Andreu Botella" href="mailto:abotella@igalia.com">
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/12617">
+<link rel="match" href="reference/text-overflow-string-008-ref.html">
+<meta name="assert" content="Test checks text-overflow ellipsis takes their bidi direction from the paragraph. With unicode-bidi: plaintext, this is the bidi paragraph's determined direction, not the value of the `direction` property.">
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+<style>
+  div {
+    font-family: monospace;
+    font-size: 10px;
+    overflow: hidden;
+    /* This custom ellipsis string has mixed LTR/RTL characters
+     * ("A" and "ום"), but its base direction (determined by the first strong
+     * char 'ו') is RTL. */
+    text-overflow: "ום A";
+    width: calc(90px + 4.1ch);
+    /* Even though the div has dir="rtl" (and therefore `direction: rtl`), its
+     * actual bidi direction is determined by its content, which is LTR. */
+    unicode-bidi: plaintext;
+  }
+  span {
+    font-family: Ahem;
+    font-size: 30px;
+  }
+</style>
+<body>
+  <p>Test passes if there is a "<strong dir="ltr">ום A</strong>" after a black rectangle below.</p>
+  <div dir="rtl">
+    <span>TestChecksThatTheBrokenContentRepalcedByBidiText</span>
+  </div>
+</body>
+</html>
