The bismuth-rich subbromide Bi₃₉Pb₉Br₄₇ = (Bi₉⁵⁺)₄[Bi₃Pb₉Br ₄₇]^20- was crystallized from a melt of bismuth, lead, and BiBr₃. X-ray diffraction on several crystals revealed a (predominantly) monoclinic structure (space group C2/m, no. 12) with lattice parameters a = 18.832(1)Å , b = 18.961(1)Å , c = 36.355(2)Å and β = 97.51(1)°. The unit cell, which contains C_4v- symmetric Bi₉⁵⁺ polycations and a complex bromido-plumbate(II)-bismuthate( III) framework, can be interpreted as one layer, which for the most part follows the tetragonal layer symmetry p4/mbm. The stacking of the layers along [001] lowers the symmetry of the structure. The high pseudosymmetry causes local disorder as well as twinning with partial pseudo-coincidence along the tetragonal c-axis. Due to small domain sizes diffuse scattering occurs. Weak maxima on the diffuse streaks can be assigned to an emerging superstructure with a period of two layers and orthorhombic symmetry, which corresponds to a repetitive polysynthetic twin with domain size of one unit cell only.