Margins too wide using a5paper Koma-Script option

Question

This is my preamble:

\documentclass[a5paper, DIV=classic, 12pt]{scrbook}
\usepackage{xltxtra,fontspec,graphicx,xunicode,color,lettrine}
\setmainfont[Mapping=tex-text, Ligatures={Rare}, Numbers=OldStyle]{ibarraReal}
\usepackage[spanish]{babel}

The problem is in the a5paper option, because I get the following

So, how can I fix the problem with margins?

Answer 1

Simply add the pagesize option:

\documentclass[a5paper, DIV=classic, 12pt, pagesize]{scrbook}

It's actually an option for typearea. If you set this option, the class sets PDF page dimensions if used with pdfLaTeX, and uses a DVI \special for the paper size if it runs in DVI mode.

It can be forced specifying the output driver, such as pagesize=pdftex, pagesize=dvips, or pagesize=dvipdfmx, however I recommend to use auto or no value, which means the same.