g-brief produces letter format PDF instead of A4 depending on system settings

I'm using g-brief to produce a letter. However, on my computer, the resulting PDF has the letter format, whereas I need A4. I figured g-brief only produces A4 PDF files, so I'm surprised. When I compile the exact same tex file on a different computer, the correct PDF in A4 format is produced. It appears that g-brief uses some sort of system setting to determine the format. I changed the content of /etc/papersize to a4, but the problem persists. Both computers run Debian (but different versions: Jessie and Wheezy).

I can force the output to A4 by using the geometry package, but then the footer disappears. How do I get LaTeX to produce the correct format?