Comparative X-ray diffraction analysis of 5,6,7,9-tetra-O-acetyl-4,8-anhydro-1,3-dideoxy-D-glycero-L-gluco-nonulose (1) and a structurally related analog, 1,2,3,4,6-penta-O-acetyl-beta-D-galactopyranose (2), are reported. Both crystals have one molecule in the unit cell and the pyranose rings in both exist in the 4C1 conformation.