diff --git a/src/vs/workbench/contrib/notebook/browser/view/renderers/webviewPreloads.ts b/src/vs/workbench/contrib/notebook/browser/view/renderers/webviewPreloads.ts
index 2397e729de4..63dbeb83997 100644
--- a/src/vs/workbench/contrib/notebook/browser/view/renderers/webviewPreloads.ts
+++ b/src/vs/workbench/contrib/notebook/browser/view/renderers/webviewPreloads.ts
@@ -839,8 +839,7 @@ function webviewPreloads() {
 
 		cellContainer.appendChild(previewContainerNode);
 
-		previewContainerNode.attachShadow({ mode: 'open' });
-		const previewRoot = previewContainerNode.shadowRoot! as any as HTMLElement;
+		const previewRoot = previewContainerNode.attachShadow({ mode: 'open' });
 
 		// Add default webview style
 		const defaultStyles = document.getElementById('_defaultStyles') as HTMLStyleElement;