  Recently Jeong and Kim [Phys. Rev. E {\bf 66}, 051605 (2002)] investigated
the scaling properties of equilibrium self-flattening surfaces subject to a
restricted curvature constraint. In one dimension (1D), they found numerically
that the stationary roughness exponent $\alpha\approx 0.561$ and the window
exponent $\delta\approx 0.423$. We present an analytic argument for general
self-flattening surfaces in $D$ dimensions, leading to $\alpha=D\alpha_0
/(D+\alpha_0)$ and $\delta=D/(D+\alpha_0)$ where $\alpha_0$ is the roughness
exponent for equilibrium surfaces without the self-flattening mechanism. In
case of surfaces subject to a restricted curvature constraint, it is known
exactly that $\alpha_0=3/2$ in 1D, which leads to $\alpha=3/5$ and
$\delta=2/5$. Small discrepancies between our analytic values and their
numerical values may be attributed to finite size effects.
