  In the rapidly expanding field of topological materials there is growing
interest in systems whose topological electronic band features can be induced
or controlled by magnetism. Magnetic Weyl semimetals, which contain linear band
crossings near the Fermi level, are of particular interest owing to their
exotic charge and spin transport properties. Up to now, the majority of
magnetic Weyl semimetals have been realized in ferro- or ferrimagnetically
ordered compounds, but a disadvantage of these materials for practical use is
their stray magnetic field which limits the minimum size of devices. Here we
show that Weyl nodes can be induced by a helical spin configuration, in which
the magnetization is fully compensated. Using a combination of neutron
diffraction and resonant elastic x-ray scattering, we find that EuCuAs develops
a planar helical structure below $T_\textrm{N}$ = 14.5 K which induces Weyl
nodes along the $\Gamma$--A high symmetry line in the Brillouin zone.
