new system call: Operation not permitted

[Aaron Brubacher]

Hi,
I'm trying to learn system calls on FreeBSD 4.2-RELEASE and I've added this system call:
int aaronflag(struct proc *p, struct aaronflag_args *uap)
{
    return 1;
}

with this entry in syscalls.master:
364     STD     BSD     { int aaronflag(); }

After running make syscalls.c and compiling, installing the kernel, when I call it with syscall(364); I get errno 1 "Operation not permitted". Any ideas what could cause this?
thanks
-Aaron