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The Defence of Mistake of Fact

Under Australian criminal law, mistake of fact is a legal defence that can be raised by a person who is charged with a strict liability offence who acted under an honest and reasonable but mistaken belief in a particular circumstance. If the court accepts that the accused had a mistaken belief and that if their mistaken belief had been correct, their actions would have been innocent, they have a full defence. This page outlines the defence of mistake of fact.

Strict liability offences

Mistake of fact is only available as a defence to offences of strict liability. Strict liability offences are offences that do not involve a mental element such as intention or recklessness. These offences rely on the accused having knowledge of the facts that give rise to the offence and in the absence of that knowledge,

How is mistake of fact established?

To successfully raise the defence of mistake of fact, the accused must establish the following elements:

  • The accused honestly and reasonably believed in certain facts which, if true, would mean that their actions were not criminal.
  • The belief of the accused person was based on reasonable grounds.
  • The accused person’s mistake of fact must relate to an essential element of the offence charged.
  • The mistake related to a matter of fact and not to a matter of law.

When can the defence of mistake of fact be used?

The defence can be relied on in response to a range of charges, including speeding, breaches of restraining orders and child sex offences. How the defence may be used in these situations is illustrated in the below examples.


An individual was discovered driving at 70km/h in an area with a speed limit of 60km/h. They claimed that according to their speedometer, they were driving at 60km/h, and thus, they could argue that they reasonably believed their speedometer to be correct. However, if they had been travelling at 100 km/h, the defence would not be successful as it would be unreasonable to believe that they were not speeding in that situation.

Breach DVO

An individual faced charges for violating a family violence order, which contained a provision that prohibited the accused from going to any premises where the protected person lived or worked. The accused was discovered at the premises where the protected person was working. However, if the accused had a valid reason to believe that the protected person did not work at the premises, they could argue that they had made an honest mistake and relied on that belief to defend themselves.

Child sex offences

An individual was accused of having sexual intercourse with a child under the age of 16. The child in question had represented themselves as being 16 years old to the accused person. However, if the accused person had a genuine but incorrect belief that the child was over 16 years old, they could argue that they made an honest mistake to defend themselves. It is important to note that this defence would be less likely to be successful if the child was actually younger, as the mistake must also be reasonable, in addition to being honest.

Case law on mistake of fact

The defence has been dealt with in a number of court decisions such as those summarized below.

Proudman v Dayman (1941)

This High Court decision established that a mistaken belief by an accused person must be a positive belief and not mere ignorance.

He Kaw Te v The Queen (1985)

This decision further established that the accused person must have expressly turned their mind to a particular fact and made the mistake. It is not sufficient that they simply did not consider the matter at all.

Mei Ying Su and Others v Australian Fisheries Management Authority and Another (2008)

This decision established that the mistake of fact defence does not involve the ‘ordinary person’ test. The belief must be a belief of the accused’s and it must be objectively reasonable. Reasonableness must  be assessed in relation to the accused’ subjective circumstances  including their personal attributes and the information they had at the time.

If you require legal advice or representation in any legal matter, please contact Armstrong Legal.

Fernanda Dahlstrom

This article was written by Fernanda Dahlstrom

Fernanda Dahlstrom has a Bachelor of Laws, a Bachelor of Arts and a Graduate Diploma in Legal Practice. She has also completed a Master’s in Writing and Literature. Fernanda practised law for eight years, working in criminal defence, child protection and domestic violence law in the Northern Territory and in family law in Queensland.

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