Variance of the t ratio Xbar over S

Let $X_1,X_2,…,X_n$ be i.i.d. $N(0,1)$ random variables, where $n>3$. If $$\bar X=\frac1n\sum_{i=1}^n X_i\quad\text{and}\quad S^2=\frac1{n-1}\sum_{i=1}^n(X_i-\bar X)^2,$$ then $\mathrm{Var}\bigl(\bar X/S\bigr)$ is equal to