  We have considered the \textit{Fermi} $\gamma$-ray light curve of the blazar
PKS 0537-441 during a high state extending from 2008/08/10 to 2011/08/27. The
periodogram exhibits a peak at T $\sim$ 280 d, with a significance of $\sim$
99.7 \%. A peak of similar relevance at $\frac{1}{2}$ T is found in the optical
light curves. Considering the entire duration of the \textit{ Fermi} light
curve 2008-2015, no significant peak is revealed, while the optical one remains
meaningful. Comparing with recent observations of PKS 2155-304 and PG 1553+113
it seems that month-year oscillations can characterize some blazars.
Month-scale oscillations can also show up only during phases of enhanced or
bursting emission like in the case of PKS 0537-441.
