Constant cell

I have two worksheets... worksheet one contains amounts...in worksheet 2 I want those amounts to be calculated with a discount in cell I1...

When I copy the formula to the cells I would like I1 to remain constant...however in following cells, it counts up...I2, I3, I4...

here is an example,

Sheet1!C7-(Sheet1!C7*Sheet2!I1)

How can I keep I1 constant?

Please help,

thanks,
Ken