  We examine the relationship between superoutburst duration $t_{\rm
  dur}$ and orbital period $P_{\rm orb}$ in AM CVn ultra-compact binary
systems. We show that the previously determined steep relation derived by
Levitan et al (2015) was strongly influenced by the inclusion of upper limits
for systems with a relatively long orbital period in their fit. Excluding the
upper limit values and including $t_{\rm dur}$ values for three systems at long
$P_{\rm orb}$ which were not considered previously, then $d \log (t_{\rm dur})/
d \log (P_{\rm orb})$ is flat as predicted by Cannizzo & Nelemans(2015)
