Let $\phi,a\in C_c^\infty(\mathbb R)$, and suppose $x_0$ is the unique critical point of $\phi$ on $\operatorname{supp}a$, with $\phi''(x_0)\ne0$. Then, as $\hbar\to0^+$, \begin{align*} \int_{\mathbb R} e^{i\phi(x)/\hbar}a(x)\,dx = e^{i\phi(x_0)/\hbar}e^{i\pi\operatorname{sgn}(\phi''(x_0))/4} \left(\frac{2\pi\hbar}{|\phi''(x_0)|}\right)^{1/2}a(x_0)+O(\hbar^{3/2}). \end{align*}