diff --git a/server.ts b/server.ts
index ba82b3e..d90405a 100644
--- a/server.ts
+++ b/server.ts
@@ -1542,7 +1542,7 @@ app.put('/api/admin/courses/:id', authenticateToken, requireAdmin, async (req: A
       data: {
         ...(title !== undefined && { title }),
         ...(description !== undefined && { description }),
-        ...(thumbnail && { thumbnailUrl: thumbnail }),
+        ...(thumbnail !== undefined && { thumbnail }),
         ...(category !== undefined && { category }),
         ...(isLocked !== undefined && { isLocked: isLocked === true || isLocked === 'true' }),
         ...(price !== undefined && { price: Number(price) }),