I need to estimate an instrumental variables regression. I have got two regressors, but I need the instrument only for one. How can I do it using the Stata?

When I use ivreg command, for example,

ivreg demand oil (demand_1=demand_2 oil_1)

I need the instrument only for demand_1, not for oil. But the Stata interprets oil as an instrument for demand_1 too.