It could well be that a workaround has already been proposed, but: $ sudo apt-get install texlive-latex-extra texlive-fonts-recommended texlive-fonts-extra texlive-base texlive-latex-base texlive-lang-greek texlive-xetex xterm git $ git clone git://git.code.sf.net/p/gretl/git gretl-git $ cd gretl-git $ sudo apt-get build-dep gretl $./configure --prefix=/usr/local --enable-quiet-build --enable-openmp --enable-build-doc $ make -j4 # all runs fine, but then ... $ make pdfdocs [...] Package natbib Warning: Citation `koenker-zhao94' on page 74 undefined on input line 6503. Package natbib Warning: Citation `koenker94' on page 74 undefined on input line 6511. Package natbib Warning: Citation `koenker-machado99' on page 74 undefined on in put line 6512. [74] ! Missing $ inserted. <inserted text> $ l.6592 ...re separated by an underscore: eg snake_ case) ? Thoughts? Cheers, Clive