http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libedit/readline/readline.h?sortby=date#rev1.42.2.1 have added two lines to readline.h: typedef int rl_hook_func_t(void); extern rl_hook_func_t *rl_event_hook; ngspice rl_event_hook had originally been defined of type void. The patch redefines the return type to be int.