Magento: Products missing old-prices, keeps lines from being straight

In grid mode displaying the products, I would like the "Add to cart" buttons to line up. But beacause only som of m开发者_高级运维y products have old-price, the once who lack it will display the button one line higher up. I have looked in prices.phtml without finding out where to edit.

td;dr: How to add a empty line in catalog if the old-price is empty?

---

Default themes have this CSS;

.products-grid .actions {
    bottom: 12px;
    position: absolute;
}

...which ensures the elements containing add to cart buttons line up.