Long arithmetic...?

It seems that a Velocity #set directive fails when the RHS involves any arithmetic operation with long integers. Specifically, I just wanted to determine the difference between two dates, thus: #set ($age = $xwiki.currentDate.time - $obj.xWikiObject.getDateValue("donedate").time) I confirmed that I got credible results from both of the operands by printing them, and I could assign either of them to another variable name, but setting $age to the result of any arithmetic operation with any of them always gave "$age" as the formatted result. This shouldn't be this hard, should it? brain[sic]