The heterotrimeric antigen 85 complex (Ag85) is a major component of the cell wall of Mycobacterium tuberculosis and consists of three abundantly secreted proteins (FbpA, FbpB and FbpC2). These play key roles in the pathogenesis of tuberculosis and in maintaining cell-wall integrity. A homologue of the Ag85 subunits (40% identity) was recently annotated in the M. tuberculosis genome as FbpC1. Unlike the Ag85-complex components, FbpC1 lacks mycolyltransferase activity and its function remains to be established. In order to aid functional characterization, FbpC1 has been crystallized. At room temperature, tetragonal crystals of FbpC1 were obtained belonging to space group P41212 (unit-cell parameters a = b = 109.9, c = 61.8 Å), yet when frozen the crystals underwent a phase transition to orthorhombic symmetry, space group P212121 (a = 59.9, b = 108.9, c = 109.9 Å). Diffraction data complete to 1.7 Å resolution were recorded at 100 K at the synchrotron.