A swellable packer for use in a subterranean well can include a seal element with a swellable material which contracts in response to temperature decrease, and a temperature compensator which applies increased force to the seal element in response to temperature decrease. A method of compensating for thermal contraction of a swellable material in a subterranean well can include a temperature of the swellable material increasing in response to installing the swellable material in the well, and a temperature compensator applying an increased force in response to a temperature decrease occurring after the temperature increasing step. A well tool for use in a subterranean well can include a swellable material and a temperature compensator which applies an increased force when the swellable material contracts.