  We prove that the largest $Q_2$-free family of subsets of $[n]$ which
contains sets of at most three different sizes has at most $(3 + 2\sqrt {3})N/3
+ o(N) \approx 2.1547N + o(N)$ members, where $N = {n \choose {\lfloor n/2
\rfloor}}$. This improves an earlier bound of $2.207N + o(N)$ by Axenovich,
Manske, and Martin.
