diff --git a/src/lib/sandbox/read-main-platform.ts b/src/lib/sandbox/read-main-platform.ts
index bc4c85f1..a8bea4b7 100644
--- a/src/lib/sandbox/read-main-platform.ts
+++ b/src/lib/sandbox/read-main-platform.ts
@@ -79,7 +79,15 @@ export const readMainInterfaces = () => {
   // and create each element to get their implementation
   const elms = Object.getOwnPropertyNames(mainWindow)
     .map((interfaceName) => createElementFromConstructor(docImpl, interfaceName))
-    .filter((elm) => elm)
+    .filter((elm) => {
+      if (!elm) {
+        return false;
+      }
+      const constructorName = getConstructorName(elm);
+      return !(
+        constructorName === 'HTMLUnknownElement' && elm.nodeName.toUpperCase() !== 'UNKNOWN'
+      );
+    })
     .map((elm) => [elm]);
 
   return readImplementations(elms, []);
diff --git a/tests/platform/custom-element/custom-element.spec.ts b/tests/platform/custom-element/custom-element.spec.ts
index 320c72ca..da544c95 100644
--- a/tests/platform/custom-element/custom-element.spec.ts
+++ b/tests/platform/custom-element/custom-element.spec.ts
@@ -7,6 +7,10 @@ test('custom-element', async ({ page }) => {
   const testDefine = page.locator('#testDefine');
   await expect(testDefine).toHaveText('TestDefineElement');
 
+  await page.waitForSelector('.testDefineOnMainAccessOnWorker');
+  const testDefineOnMainAccessOnWorker = page.locator('#testDefineOnMainAccessOnWorker');
+  await expect(testDefineOnMainAccessOnWorker).toHaveText('it works');
+
   await page.waitForSelector('.testNoReDefine');
   const testNoReDefine = page.locator('#testNoReDefine');
   await expect(testNoReDefine).toHaveText('TestNoReDefineElement');
diff --git a/tests/platform/custom-element/index.html b/tests/platform/custom-element/index.html
index f93ea1ce..6eb11bf6 100644
--- a/tests/platform/custom-element/index.html
+++ b/tests/platform/custom-element/index.html
@@ -57,6 +57,10 @@
         logScriptExecution: true,
       };
     </script>
+    <script type="text/javascript">
+      class TestDefineOnMainAccessOnWorker extends HTMLElement {}
+      customElements.define('define-on-main-access-on-worker', TestDefineOnMainAccessOnWorker);
+    </script>
     <script src="/~partytown/debug/partytown.js"></script>
   </head>
   <body>
@@ -79,6 +83,19 @@ <h1>Custom Element</h1>
         </script>
       </li>
 
+      <li>
+        <strong>define on main, access on worker</strong>
+
+        <define-on-main-access-on-worker id="testDefineOnMainAccessOnWorker"></define-on-main-access-on-worker>
+        <script type="text/partytown">
+          (function () {
+            const elm = document.getElementById('testDefineOnMainAccessOnWorker');
+            elm.textContent = 'it works';
+            elm.className = 'testDefineOnMainAccessOnWorker';
+          })();
+        </script>
+      </li>
+
       <li>
         <strong>no worker re-define</strong>
         <div id="testNoReDefine"></div>
