On the average of the number of imaginary quadratic fields with a given class number

Let $\mathcal{F}(h)$ be the number of imaginary quadratic fields with class number $h$. In this note, we improve the error term in Soundararajan's asymptotic formula for the average of $\mathcal{F}(h)$. Our argument leads to a similar refinement of the asymptotic for the average of $\mathcal{F}(h)$ over odd $h$, which was recently obtained by Holmin, Jones, Kurlberg, McLeman and Petersen.