Question about Chromosomes and Evolution?

Chimps, gorillas, and bonobos have 48 chromosomes. Humans have 46 chromosomes. Evolution says that 2 of the chromosomes of our ancient ape ancestor "fused", and thats how we got 46. But when i do the math, if 2 of the chromosomes fused to make 1 chromosome, wouldn't we have 47 chromosomes? I mean, technically, our ancestor only 'lost' 1 chromosome, right?