jQuery error whan using gform_post_paging

I need to modify the number displayed in progressbar title dynamically in a multipage form and I use this hook gform_post_paging for this purpose.

However, I get an error when I call this on the subsequent pages:
jQuery('.gf_progressbar_title').text('Step 2 af 3');
Firbug tells me that jQuery is not defined.

Any idea of how I can fix this?

Thanks
Vayu

Hi David.
Thanks for helping, I have also tried that, but it causes the same error.