A mistake is a false assumption made by one or both parties in the formation of a contract and may be used as grounds to invalidate the agreement. There are three types of mistake in the law of contract. These are common mistake, mutual mistake and unilateral mistake. A common mistake is where both parties hold the same mistaken beliefs of the facts. A common mistake ca only void a contract if the mistake of the subject matter was sufficiently fundamental to render its identity different from what was contracted, making the performance of the contract impossible. There are two situations of common mistake. These are the case of res extincta and the case of res sua. In the case of res extincta, there is a common mistake asto the existence of the subject matter of the contract. For example, if A agrees to sell his car to B and unknown to both persons, the car had at the time of sale been destroyed by fire, the contract will be void because A has innocently undertaken an obligation which he cannot possibly fulfill. The following case is an application of res extincta. In the case of Couturier v Hastie, Hastie dispatched a cargo of corn from Salonica and sent the chaterparty a bill of lading to their London agents so that the corn might be sold. The London agents employed Couturier to sell the corn and a person named Callander bought it. Unknown to the parties the cargo had become overheated and had been landed at the nearest port and sold, so that when the contract was made the corn was not really in existence. Callander repudiated the contract and Couturier was sued because he was a del credere agent, that is, an agent who, for an extra commission, undertakes to indemnify his principal against losses arising out of the repudiation of the contract by any third party introduced to him. It was held that the claim against Couturier failed because the contract