Testing results from inputbox for a date

I have this code

start_date1 = Application.InputBox("Enter date for which this data applies.  If the data applies to April  2011 then input 4/1/11.")
If start_date1 = "" Then GoTo end_qrybcklog

Note: end_qrybcklog is at the end of the subroutine.

Problem is that then the "if" gets executed i get a run-time error.

how to test input from inputbox. if user hits cancel i want to exit.