From the feedback of the channel state information (CSI), precoding techniques improve the performance of multiple-input multiple-output (MIMO) systems by optimizing various criteria. In this correspondence, an efficient precoder that maximizes the minimum distance (dmin) of two received vectors is studied. This criterion leads to a nondiagonal precoding scheme and allows achieving a full diversity order. However, the optimized solution for MIMO systems using a high-order QAM modulation is rather complex and changes for different constellations. Therefore, we propose herein a general form of minimum Euclidean distance based precoders for all rectangular QAM modulations. It is shown that the new solution optimizes the distance dmin for small and large dispersive channels.