Not enough stock but still able to check out?

There is this statement in my Shopping Cart (before I click Checkout):

Products marked with *** are out of stock or .
Items not in stock will be placed on backorder.

I have set my items to qty available - 1 pc,
I try to add 3pc to cart and it shows the statement above.
User is still able to check out and complete the order process..

Is there anyway that I can stop the user from checking out if the stocks are not enough?

There is this statement which i found in shopping_cart.php :

define('OUT_OF_STOCK_CANT_CHECKOUT', 'Products marked with ' . STOCK_MARK_PRODUCT_OUT_OF_STOCK . ' are out of stock or there are not enough in stock to fill your order.<br />Please change the quantity of products marked with (' . STOCK_MARK_PRODUCT_OUT_OF_STOCK . '). Thank you');
define('OUT_OF_STOCK_CAN_CHECKOUT', 'Products marked with ' . STOCK_MARK_PRODUCT_OUT_OF_STOCK . ' are out of stock or .<br />Items not in stock will be placed on backorder.');

I suppose is to change some codes to like only 'OUT_OF_STOCK_CANT_CHECKOUT' or is there anything i need to change in the admin configuration?

Admin > Configuration > Stock