Sort by ACTUAL price

Hi
In my main website, I use links to display the result of a search for a particular type of product in my Opencart store pre-sorted - usually by price low-high.
However, I notice that the sorting only takes into account the original pre-special offer price which means that a product that is on 'special' at the cheapest price, would appear at the bottom of the list if the pre-special price is the highest.
Is there any way to modify a sorted search to take into account special prices?
I am using v.1.5.2.1