  The magnetic structure of the heavy fermion antiferromagnet CePt$_2$In$_7$ is
determined using neutron diffraction. We find a magnetic wave vector
$\mathbf{q}_M = (1/2,1/2,1/2)$, which is temperature independent up to $T_N =$
5.5 K. A staggered moment of 0.45(1)$\mu_B$ at 2 K resides on the Ce ion. The
nearest-neighbor moments in the tetragonal basal plane are aligned
antiferromagnetically. The moments rotate by 90$^\circ$ from one CeIn$_3$ plane
to another along the $c$ axis. A much weaker satellite peak with an
incommensurate magnetic wave vector $\mathbf{q}_M = (1/2,1/2,0.47)$ seems to
develop at low temperature. However, the experimental data available so far are
not sufficient to draw a definitive conclusion about the possible co-existence
of commensurate and incommensurate magnetic structures in this material.
