The crystal structure of α‐Fe2O3 and α‐Cr2O3 is usually described with the corundum‐type trigonal crystal structure based on the space group . There are, however, some observations of the magnetic ordering of both α‐Fe2O3 and α‐Cr2O3 that are incompatible with the trigonal symmetry. We show experimental evidence based on X‐ray powder diffraction and supported by transmission electron microscopy that the symmetry of the crystal structure of both α‐Fe2O3 and α‐Cr2O3 is monoclinic and it is described with the space group C2/c (derived from by removing the threefold rotation axis). The magnetic orderings of α‐Fe2O3 and α‐Cr2O3 are compatible with the magnetic space groups C2/c and C2/c′, respectively. These findings are in agreement with the idea from Curie [(1894), J. Phys.3, 393–415] that the dissymmetry of the magnetic ordering should be associated with a dissymmetry of the crystal structure.