diff --git a/testing/web-platform/tests/dom/nodes/moveBefore/tentative/Node-moveBefore.html b/testing/web-platform/tests/dom/nodes/moveBefore/tentative/Node-moveBefore.html
index a23678082669..64a76602d264 100644
--- a/testing/web-platform/tests/dom/nodes/moveBefore/tentative/Node-moveBefore.html
+++ b/testing/web-platform/tests/dom/nodes/moveBefore/tentative/Node-moveBefore.html
@@ -221,11 +221,22 @@
   a.append(b);
   a.append(c);
   assert_array_equals(a.childNodes, [b, c]);
-  assert_equals(a.moveBefore(b, b), b);
+  assert_equals(a.moveBefore(c, b), undefined, "moveBefore() returns undefined");
+  assert_array_equals(a.childNodes, [c, b]);
+}, "moveBefore() returns undefined");
+
+test(() => {
+  const a = document.body.appendChild(document.createElement("div"));
+  const b = document.createElement("div");
+  const c = document.createElement("div");
+  a.append(b);
+  a.append(c);
+  assert_array_equals(a.childNodes, [b, c]);
+  a.moveBefore(b, b);
   assert_array_equals(a.childNodes, [b, c]);
-  assert_equals(a.moveBefore(c, c), c);
+  a.moveBefore(c, c);
   assert_array_equals(a.childNodes, [b, c]);
-}, "Inserting a node before itself should not move the node");
+}, "Moving a node before itself should not move the node");
 
 test(() => {
   const disconnectedOrigin = document.createElement('div');