Index: sys/riscv/riscv/trap.c
===================================================================
--- sys/riscv/riscv/trap.c
+++ sys/riscv/riscv/trap.c
@@ -98,29 +98,33 @@
 	struct proc *p;
 	register_t *ap;
 	struct syscall_args *sa;
-	int nap;
+	bool shift_args;
 
-	nap = NARGREG;
 	p = td->td_proc;
 	sa = &td->td_sa;
 	ap = &td->td_frame->tf_a[0];
 
 	sa->code = td->td_frame->tf_t[0];
 
-	if (sa->code == SYS_syscall || sa->code == SYS___syscall) {
+	if (__predict_false(sa->code == SYS_syscall || sa->code == SYS___syscall)) {
 		sa->code = *ap++;
-		nap--;
+		shift_args = true;
+	} else {
+		shift_args = false;
 	}
 
-	if (sa->code >= p->p_sysent->sv_size)
+	if (__predict_false(sa->code >= p->p_sysent->sv_size))
 		sa->callp = &p->p_sysent->sv_table[0];
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
 	sa->narg = sa->callp->sy_narg;
-	memcpy(sa->args, ap, nap * sizeof(register_t));
-	if (sa->narg > nap)
-		panic("TODO: Could we have more then %d args?", NARGREG);
+	KASSERT(sa->callp->sy_narg <= nitems(sa->args), ("Too many syscall arguments!"));
+
+	if (__predict_false(shift_args))
+		memcpy(sa->args, ap, (NARGREG - 1) * sizeof(register_t));
+	else
+		memcpy(sa->args, ap, NARGREG * sizeof(register_t));
 
 	td->td_retval[0] = 0;
 	td->td_retval[1] = 0;