Defence of Honest and Reasonable Mistake of Fact

When is the defence available?

The defence of honest and reasonable mistake of fact can be used for strict liability offences. A strict liability offence is a crime that does not require that the accused had a guilty mind.

An example of a strict liability offence is driving without a licence. It does not matter if the accused person did not intend to drive without a licence as guilt can be established by the act itself.

An accused who commits a strict liability offence will avoid liability where they had an honest and reasonable belief in the existence of facts, if true, would have made his/her/their conduct entirely lawful. This guiding principle was set out in the case of Proudman v Dayman.1

Will the defence succeed?

This defence consists of three elements:

  1. Was the mistake honest (subjective test); and
  2. Was the mistake reasonable (objective test); and
  3. Was it based on a mistake of fact, rather than law.
Was the mistaken matter considered by the accused?

The case of He Kaw Teh v The Queen2 establishes the requirement for the accused to have considered a particular fact relating to their matter and made an honest mistake about it which is reasonable in the circumstances.

For example, if you have been charged with driving an unregistered vehicle and you simply forgot to renew your car registration, the defence will not apply. In order for this defence to apply, you must have done more than just not considered the matter at all.

Compare this to a scenario where you renewed your licence but due to an administrative error with VicRoads, your licence had not renewed in their system. The defence may be applicable in this situation because you held an honest and reasonable belief, based on your own due diligence, that you held a licence.

Ignorance of the law

The defence does not apply to a mistake of law or ignorance of law as shown by the case of Ostrowski v Palmer.3 If you were not aware that driving an unregistered vehicle is against the law, this defence will not be available to you.

Who can raise the defence?

You, as the accused person, must raise this defence if you intend to rely on it. It is not a process that happens automatically. Once it has been raised, the prosecution can try to show that the mistake was not honest, not reasonable or was not a mistake of fact.

Your matter

If you have questions about whether this defence is available to you, call our office to speak with one of our experienced criminal lawyers. Every case is different which means it takes a criminal lawyer to identify the situations in which the defence applies.

For more information, read our blog article on the defence of honest and reasonable mistake of fact.


[1] Proudman v Dayman [1941] 67 CLR 536
[2] He Kaw Teh v The Queen [1985] HCA 43
[3] Ostrowski v Palmer [2004] HCA 30