Countif formula help

Hi,

I'm hoping someone can help.

I'm trying to add a formula which will count the number of cells where the following is true:

Column D = "3"
Column G has a date input which is before a date in cell G13

Hope this makes sense!!

I've tried:
=COUNTIFS(D16:D40,3,G16:G40,"<G13")

But, when i've added the 3 to column D and the date stated in column G is before the date in G13 - the cell shows a '0' instead of a '1'

I am using another formula to find the date in G13 - could that be an issue?

Thank you in advance for any help you can offer me!

Lisa