[en] The room-temperature phase of K₂ZnBr₄ is isomorphous with Sr₂GeS₄ (P2₁/m) while the low-temperature structure (P2₁) is slightly distorted [the phase transition occurs at 155 K]. Both structures contain highly deformed tetrahedral [ZnBr₄]^2- molecules with Br(3)-Zn-Br(3') angles of 103.06(5) and 102.49(9) at 291 and 144 K, respectively. This distortion is caused by the repulsion of Br atoms whose distance 3.712(1) and 3.661(2) A at 291 and 144 K, respectively, is below the Br-Br van der Waals distance (3.9 A). The phase transition is accompanied by minor shifts of cations and [ZnBr₄]^2-tetrahedra which are simultaneously rotated about a small angle. Below the phase transition point an inversion twin develops whose twin-fraction parameter was refined to 0.459(65). (orig.)