SUMIF formula for subracting

I'm looking for a formula that that will subtract two cells if the value of one cell is greater than 0.

Details:
Cell B1 contains a value of 25 (Note this value never changes)
Cell B2 contains a value of 0 (Note this value will change)

I need a formula that states: if B2 is 0 display 0, but if B2 contains a number greater than 0 then subtract B2 from B1.

Re: SUMIF formula for subracting

Thanks Derk, that worked (guess I was trying to complicate the equation, thanks again).