diff --git a/shadow-dom/declarative/clonable.window.js b/shadow-dom/declarative/clonable.window.js
index 5ebeacf37cbd8ab..c324d10681b4d28 100644
--- a/shadow-dom/declarative/clonable.window.js
+++ b/shadow-dom/declarative/clonable.window.js
@@ -8,3 +8,29 @@ test(() => {
   assert_equals(cloned.shadowRoot.children.length, 1, "children count");
   assert_equals(cloned.shadowRoot.children[0].localName, "input", "children content");
 }, "attachShadow with clonable: true");
+
+for (clonable of [false, undefined]) {
+  test(() => {
+    const div = document.createElement("div");
+    const root = div.attachShadow({ mode: "open", clonable });
+    root.appendChild(document.createElement("input"));
+    assert_false(root.clonable, "clonable attribute");
+
+    const cloned = div.cloneNode(true);
+    assert_true(!cloned.shadowRoot, "shadow should not be cloned");
+  }, `attachShadow with clonable: ${clonable}`);
+}
+
+test(() => {
+  const div = document.createElement("div");
+  div.setHTMLUnsafe('<div><template shadowrootmode=open><input></template></div>');
+  const root = div.firstElementChild.shadowRoot;
+  assert_true(!!root);
+  assert_true(root.clonable, "clonable is automatically true for declarative shadow root");
+
+  const cloned = div.cloneNode(true);
+  const clonedRoot = cloned.firstElementChild.shadowRoot;
+  assert_true(!!clonedRoot);
+  assert_equals(clonedRoot.children.length, 1, "children count");
+  assert_equals(clonedRoot.children[0].localName, "input", "children content");
+}, "declarative shadow roots get clonable: true automatically");