Report with Grouping

Dear All,
I have a very simple report with 2 dataitems say Sales Herader and Sales Line. I grouped the Sales Line records for Sales Order nO.
Now i want that page Breaks should not separate all data pertaining to an Order Number, it should be on the same page, not split between two pages.
Eg. if a Sales Order has four lines, and a report has only two lines left to print in a page, then the entire group should move to next page instead of splitting over 2 pages.