I have a black moor, is it okay to add another goldfish to the tank?

I've had a black moor in a tank by itself for about 4 months now, and today i got another goldfish (it's a white one if that makes a difference) and i don't know if its okay for me to put the two together. when i bought the black moor it was in a tank with several other goldfish, but after living alone for several months, i don't want it to think the other goldfish is food. the black moor is about 3 inches long and the new goldfish is about an inch, so they are of very different sizes.