In this paper, a method to decrease the size of location map for non-overlapping pattern substitution method is presented. Original pattern substitution (PS) method has been proposed by Ho et al. as a reversible watermarking scheme for binary images. They use a pair of two patterns to embed data. Unfortunately, their location map is huge in size. In our method, we propose an efficient mechanism which can decrease the size of location map considerably for un-overlapping version of the PS method. Experiment results show that our method works well on decreasing the size of location map. Comparison results with the original PS method demonstrate that the proposed method achieves more embedding capacity and higher PSNR value due to the reduced size of the location map.