A gas spring has a closed cylinder, the interior of which is divided into a first working space and a second working space by a piston, which is free to slide back and forth in the cylinder. The piston has a piston rod, which extends through the second working space and out from the cylinder through a seal. The first working space and the second working space are filled with pressurized gas. A compensating space, which is filled with a compensating medium, is also provided. The volume of this compensating medium changes with the temperature, and this change in volume brings about a corresponding change in the volume of the first working space. The compensating medium is an incompressible medium which expands in volume as the temperature drops, this expansion leading to a decrease in the volume of the first working space.