This paper concerns the design of codes for multiple-input multiple-output communication systems. The transmission scheme utilizes imperfect channel state information (CSI) in the design, assuming that maximum-likelihood detection is employed at the receiver. It is argued that channel diagonalizing codes are not robust to imperfections in the CSI. A robust non-diagonalizing code with good minimum distance separation between received codewords is proposed. The design is very suitable for systems operating at high data rates since the complexity scales nicely with the number of antennas. Numerical results show that the proposed code outperforms a state-of-the-art diagonalizing precoder.