Devices, systems and methods for video processing are described. In one aspect, a video processing method is provided to include determining, for a conversion between a current video block of a video and a coded representation of the video, that a motion information of the current video block is refined using an optical flow-based method in which at least one motion vector offset is derived for a region within the current video block; clipping the at least one motion vector offset to a range [−N,M], wherein N and M are integers based on a rule; and performing the conversion based on at least one clipped motion vector offset.