Integral2 weird phenomenon (NEED HELP)

So, I have encountered a weird phenomenon when using the integral2 function.

I call integral2 in the following manner:

ymax=0.03648*10^9;

xmin= 1.0949;

w=2000;

z=1.0631;

fun=@(x,y) fun1(x,y,w,z) * fun2(x) * x^4;

ans=integral2(fun,xmin,inf,0,ymax);

Now what happens is that for example I know the result of this should be 0.9, instead of getting that I get a value equal to 0.9*ymax.

I checked all the intermediate values I could and I get the right values for all of them but at some point I guess it multiplies the final answer by ymax and I can't figure out why. Any ideas would be much appreciated.

Thanks!