  Let $\Omega^+\subset\mathbb R^{n+1}$ be a bounded $\delta$-Reifenberg flat
domain, with $\delta>0$ small enough, possibly with locally infinite surface
measure. Assume also that $\Omega^-= \mathbb R^{n+1}\setminus
\overline{\Omega^+}$ is an NTA domain as well and denote by $\omega^+$ and
$\omega^-$ the respective harmonic measures of $\Omega^+$ and $\Omega^-$ with
poles $p^\pm\in\Omega^\pm$. In this paper we show that the condition that
$\log\dfrac{d\omega^-}{d\omega^+} \in VMO(\omega^+)$ is equivalent to
$\Omega^+$ being a chord-arc domain with inner normal belonging to
$VMO(H^n|_{\partial\Omega^+})$.
