We describe a simple modification of the so-called Weighted Stego Image (WS) steganalysis method, due to Fridrich and Goljan, to detect sequential replacement of least significant bits. The most sensitive methods for the detection of bit replacement do not work well when the payload is concentrated at the start of the cover instead of being spread evenly over it, so this detector fills a gap in the literature. Experimental results show that the adapted method gives sequentially-embedded payload estimation typically 10 times more accurate than the standard WS method.