You have a chance of getting it to work, and even then, it may have stability issues. When manufactuer makes a kit, it needs more testing and quality control than a single stick does to guarentee it will work together. This testing is not done on single sticks which is why, even when buying identical moduals, you are not guarenteed for it to work. I reccomend buying a new kit, and seeing if it will work even with the extra stick, this way if you're luckey you'll have more RAM and even if your not, you won't be down the cost of a single stick that turned out not to work.