Error performance is one of the main performance measures and derivation of its closed-form expression has proved to be quite involved for certain systems. In this letter, a unified closed-form expression, applicable to different binary modulation schemes, for the bit error rate of dual-branch selection diversity based systems undergoing independent but not necessarily identically distributed generalized-K fading is derived in terms of the extended generalized bivariate Meijer G-function. ; Comment: Diversity schemes, selection combining, dual-branch selection diversity, binary modulation schemes, generalized-K (GK) model, composite fading, bit error rate (BER), and Meijer G-function distribution