This paper analyzes the performance of the recently proposed quadrature spatial modulation (QSM) multipleâ€“input multipleâ€“output (MIMO) system over Nakagamiâ€“m fading channel. In the analysis, the general distribution of the Nakagamiâ€“m channel phase is considered. In the literature, performance analysis of spatial modulation (SM) over Nakagamiâ€“m channel with uniform phase is conducted. However, apart from the very special case of m = 1, where Nakagamiâ€“m fading corresponds to Rayleigh fading, the phase of the Nakagamiâ€“m distribution is not uniformly distributed. It is shown in this paper that the phase of the channel has major impact on the performance of spatial multiplexing MIMO systems such as SM and QSM systems. A general upper bound expression for the average bit error ratio (ABER) performance of QSM is derived and the impact of different channel parameters is studied. Monte Carlo simulation results are provided to corroborate the exactness of the derived analysis.