Sumproduct & Sumif formula to only add up values <0

Hi there,

I have the following formula:

=SUMPRODUCT(SUMIF(Data!A:A,$G$4:$O$4,Data!G:G),$G5:$O5)

I basically want this formula to do what it's currently doing, however only add up cells <0 only.

The above formula is giving a cumalative total, so -20, -30, -50, 150 would = 50....I need it to show -100.

Hope this makes sense. I can post my spreadsheet if not.

Many thanks

Sam