Networks of OH⋯O bonds in sugars and H₂O ices are hardly affected by temperature, but transform under pressure. Such a transition at 1.95 GPa in β-D-mannose induces strong strain, non-destructive for the single crystal and easily visible in its shape deformation. This transition occurs at the lowest pressure of all sugars investigated at high pressure so far. The giant strain propagates perpendicular to the clearly visible zero-strain planes. The transition reconstructs the 3-dimensional pattern of OH⋯O hydrogen bonds, changes the conformation of molecules and preserves the space-group symmetry, like the analogous transitions of α-D-glucose and D-sucrose. However, new repulsing O⋯O contacts have been generated at high pressure in D-mannose only.