sql update comand syntax

I need to update one table based on data in a second. TFM doesn't have example exactly that I need. I have tried arranging the syntax in a couple of differnt ways, with no luck. I am new to informix but have a tight deadline. here it is update award set award.AWARD_AMOUNT = award.AWARD_AMOUNT + award.CARRY_FORWARD where award.AWARD_ACCOUNT = mod.MOD_ACCOUNT and (mod.MOD_PROCESSING = "2X" or mod.MOD_PROCESSING = "CL"); I have tried using a select statement before the where clause, but the data being modified is not coming from mod table, just mod table has the criterie for the update of award table. Help.