diff --git a/src/controllers/CartController.ts b/src/controllers/CartController.ts
index 2e13696..3dbd652 100644
--- a/src/controllers/CartController.ts
+++ b/src/controllers/CartController.ts
@@ -12,7 +12,7 @@ export async function addToCart(req: Request, res: Response) {
       res.status(400).json({ error: 'Product id is required.' });
       return;
     }
-    let cart: ICart = await Cart.findOne({ userId });
+    let cart: ICart | null = await Cart.findOne({ userId });
     if (!cart) {
       cart = await Cart.create({
         userId,