/* XXX this is actually forward-static. */ extern struct command db_show_cmds; Try again. Okay, I did. This time it stopped with exactly the same error for these two files: sys/kern/subr_prf.c: static int msgbufmapped; sys/sys/msgbuf.h: extern int msgbufmapped; I really don't understand how I compiled the same code yesterday with the same compiler! Did you do something sneaky like change warnings to errors?