  We use Kepler short cadence light curves to constrain the oblateness of
planet candidates in the Kepler sample. The transits of rapidly rotating
planets that are deformed in shape will lead to distortions in the ingress and
egress of their light curves. We report the first tentative detection of an
oblate planet outside of the solar system, measuring an oblateness of $0.22 \pm
0.11$ for the 18 $M_J$ mass brown dwarf Kepler 39b (KOI-423.01). We also
provide constraints on the oblateness of the planets (candidates) HAT-P-7b,
KOI-686.01, and KOI-197.01 to be < 0.067, < 0.251, and < 0.186, respectively.
Using the Q'-values from Jupiter and Saturn, we expect tidal synchronization
for the spins of HAT-P-7b, KOI-686.01 and KOI-197.01, and for their rotational
oblateness signatures to be undetectable in the current data. The potentially
large oblateness of KOI-423.01 (Kepler 39b) suggests that the Q'-value of the
brown dwarf needs to be two orders of magnitude larger than that of the solar
system gas giants to avoid being tidally spun-down.
