diff --git a/apps/web/src/components/editor/lesson-content-viewer.tsx b/apps/web/src/components/editor/lesson-content-viewer.tsx
index feebec7..67ee69a 100644
--- a/apps/web/src/components/editor/lesson-content-viewer.tsx
+++ b/apps/web/src/components/editor/lesson-content-viewer.tsx
@@ -57,7 +57,7 @@ export function LessonContentViewer({ content, className }: LessonContentViewerP
     if (!containerRef.current || !content) return;
     const mermaidNodes = containerRef.current.querySelectorAll('pre[data-language="mermaid"]');
     if (mermaidNodes.length === 0) return;
-    mermaid.run({ nodes: Array.from(mermaidNodes), suppressErrors: true }).catch(() => {});
+    mermaid.run({ nodes: Array.from(mermaidNodes) as HTMLElement[], suppressErrors: true }).catch(() => {});
   }, [content]);
 
   if (!editor) return null;