Created attachment 1936748 [details] bib2html-c99.patch In order to avoid build failures with future compilers, we need to add proper function prototypes to the generated parser and lexer. The sources already hint to this, but automake is generally quite poor at supporting this. What works in my experience is to add the required prototypes to some header file that is included everywhere (including the generated lexer/parser sources, so that the manually written declarations are checked against the implementation). Tracking this here because upstream seems to be inactive.