diff --git a/shadow-dom/declarative/declarative-shadow-dom-repeats.html b/shadow-dom/declarative/declarative-shadow-dom-repeats.html
index 9cee41f2f3160e..a2bfa488fb76f3 100644
--- a/shadow-dom/declarative/declarative-shadow-dom-repeats.html
+++ b/shadow-dom/declarative/declarative-shadow-dom-repeats.html
@@ -55,7 +55,7 @@
 </script>
 
 <div id=open2>
-  <template shadowrootmode=open shadowrootdelegatesfocus shadowrootclonable serializable>
+  <template shadowrootmode=open shadowrootdelegatesfocus shadowrootclonable shadowrootserializable>
     Open, delegates focus (not the default), clonable (not the default)
     serializable (not the default), named slot assignment (the default)
   </template>
diff --git a/shadow-dom/declarative/gethtml.tentative.html b/shadow-dom/declarative/gethtml.tentative.html
index eabd39131ba627..c03749c815c5ed 100644
--- a/shadow-dom/declarative/gethtml.tentative.html
+++ b/shadow-dom/declarative/gethtml.tentative.html
@@ -36,7 +36,7 @@
       default: throw new Error(`Invalid serializable ${serializable}`);
     }
     const delegatesAttr = delegatesFocus ? ' shadowrootdelegatesfocus=""' : '';
-    const serializableAttr = expectedSerializable ? ' serializable=""' : '';
+    const serializableAttr = expectedSerializable ? ' shadowrootserializable=""' : '';
     const clonableAttr = clonable ? ' shadowrootclonable=""' : '';
 
     if (allowsShadowDom && declarativeShadowDom) {