Prawn does not render a PDF on Heroku, but does it local

As the title says: My PDFs are perfectly rendered when I run on my server locally, but on Heroku I get a NoMethodError. It seems that Heroku cannot find my prawn gem. I am using t开发者_StackOverflow中文版he prawn-rails gem.

Any ideas?

I have uploaded the complete callstack here: http://f.cl.ly/items/2g232h3U0B2G0k0i0S1y/Action%20Controller%20%20Exception%20caught.html

Solved. It seems as Heroku does not have a "Helvetica".