Zero divided by zero error - need help

Not sure why this is returning such a strange result:

Expenses YOY % = IF([Expenses Prior Year]=0,BLANK(),DIVIDE([Expenses]-[Expenses Prior Year],[Expenses Prior Year]))

The curent year expenses in this category are $20,655.12. The prior year's expenses in this category were zero. I am trying to get the percentage increase in expenses. 

The result I get is 394965993271454000%.

Thanks.