Problem with integrate and wave matching..

I use the following commands(latest version):

•make/o/d/n=(1000) testgauss = 100*exp(-.5*(p-500)^2/900)
•make/o/d/n=(1000) gauss_x = p
•integrate testgauss /x=gauss_x /d=areagauss

and get the following error:

X data does not match Y data (length or number type)


What am I doing wrong?
EDIT: Nevermind, help files are our friends. X data must be one point longer than Y data for it to "match" in length.