An approach for improving the compression performance of an existing chaos-based joint compression and encryption scheme is proposed. The lookup table used for encryption is dynamically updated in the searching process. Once a partition not matched with the target symbol is visited, this and other partitions mapped to the same symbol are reallocated to a nonvisited symbol. Therefore, the target symbol eventually associates with more partitions and fewer number of iterations are needed to find it. As a result, expansion of the ciphertext is avoided, and the compression ratio is improved. Simulation results show that the proposed modification leads to a better compression performance, whereas the execution efficiency is comparable. The security of the modified scheme is also analyzed in detail.