ROW_NUMBER() in linqpad

I am trying to get row numbers to show up in my LINQPad query.

SELECT ROW_NUMBER() OVER(ORDER BY TestNum) AS 'Row Number', TestNum
FROM Test

I get:

Error 195: 'ROW_NUMBER' is not a recognized function name.

I also tried

ROWNUM()

{ fn ROW_NUMBER() }

{ fn ROWNUM() }

among others...

I am using LINQPad v4.20

Thanks.

What version of SQL Server are you using? ROW_NUMBER() is not available in SQL Server 2000 or earlier.