INDIRECT cell reference - Can't copy cell as reference cell pattern remains same

I have an Overview Sheet where I want to display a sum of values from another sheet. I'm using the indirect function to grab the sheet name from a cell in the overview sheet. The formula looks like this and sits in Cell C16:

=SUM(INDIRECT($A17&"!B$2:B"))

When I now copy the cell to the next column (D16) the reference should adjust like so:

=SUM(INDIRECT($A17&"!C$2:C"))

But it doesnt, it just remains as is. How do I get the formula to adjust the text part in the INDIRECT function as well?

Thanks