CACI No. 330. Affirmative Defense - Unilateral Mistake of Fact
Judicial Council of California Civil Jury Instructions (2023 edition)
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330.Affirmative Defense - Unilateral Mistake of Fact
[Name of defendant] claims that there was no contract because [he/she/
nonbinary pronoun/it] was mistaken about [insert description of mistake].
To succeed, [name of defendant] must prove all of the following:
1. That [name of defendant] was mistaken about [insert description of
mistake];
2. That [name of plaintiff] knew [name of defendant] was mistaken
and used that mistake to take advantage of [him/her/nonbinary
pronoun/it];
3. That [name of defendant]’s mistake was not caused by [his/her/
nonbinary pronoun/its] excessive carelessness; and
4. That [name of defendant] would not have agreed to enter into the
contract if [he/she/nonbinary pronoun/it] had known about the
mistake.
If you decide that [name of defendant] has proved all of the above, then
no contract was created.
New September 2003; Revised April 2004
Directions for Use
If the mistake is one of law, this may not be a jury issue.
This instruction does not contain the requirement that the mistake be material to the
contract because the materiality of a representation is a question of law. (Merced
County Mutual Fire Insurance Co. v. State of California (1991) 233 Cal.App.3d
765, 772 [284 Cal.Rptr. 680].) Accordingly, the judge would decide whether an
alleged mistake was material, and that mistake would be inserted into this
instruction.
Sources and Authority
• When Consent Not Freely Given. Civil Code sections 1567, 1568.
• Mistake. Civil Code section 1576.
• Mistake of Fact. Civil Code section 1577.
• “It is settled that to warrant a unilateral rescission of a contract because of
mutual mistake, the mistake must relate to basic or material fact, not a collateral
matter.” (Wood v. Kalbaugh (1974) 39 Cal.App.3d 926, 932 [114 Cal.Rptr. 673].)
• “A mistake need not be mutual. Unilateral mistake is ground for relief where the
mistake is due to the fault of the other party or the other party knows or has
reason to know of the mistake. . . . To rely on a unilateral mistake of fact, [the
party] must demonstrate his mistake was not caused by his ‘neglect of a legal
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duty.’ Ordinary negligence does not constitute the neglect of a legal duty as that
term is used in section 1577.” (Architects & Contractors Estimating Service, Inc.
v. Smith (1985) 164 Cal.App.3d 1001, 1007-1008 [211 Cal.Rptr. 45], internal
citations omitted.)
• To prevail on a unilateral mistake claim, the defendant must prove that the
plaintiff knew that the defendant was mistaken and that plaintiff used that
mistake to take advantage of the defendant: “Defendants contend that a material
mistake of fact - namely, the defendants’ belief that they would not be obligated
to install a new roof upon the residence - prevented contract formation. A
unilateral mistake of fact may be the basis of relief. However, such a unilateral
mistake may not invalidate a contract without a showing that the other party to
the contract was aware of the mistaken belief and unfairly utilized that mistaken
belief in a manner enabling him to take advantage of the other party.” (Meyer v.
Benko (1976) 55 Cal.App.3d 937, 944 [127 Cal.Rptr. 846], internal citations
omitted.)
• “Failure to make reasonable inquiry to ascertain or effort to understand the
meaning and content of the contract upon which one relies constitutes neglect of
a legal duty such as will preclude recovery for unilateral mistake of fact.” (Wal-
Noon Corporation v. Hill (1975) 45 Cal.App.3d 605, 615 [119 Cal.Rptr. 646].)
However, “[o]rdinary negligence does not constitute the neglect of a legal duty
as that term is used in section 1577.” (Architects & Contractors Estimating
Service, Inc. v. Smith, supra, 164 Cal.App.3d at p. 1008.)
• Neglect of legal duty has been equated with “gross negligence,” which is defined
as “the want of even scant care or an extreme departure from the ordinary
standard of conduct.” (Van Meter v. Bent Construction Co. (1956) 46 Cal.2d 588,
594 [297 P.2d 644].)
Secondary Sources
1 Witkin, Summary of California Law (11th ed. 2017) Contracts, §§ 257-276
17 California Forms of Pleading and Practice, Ch. 215, Duress, Menace, Fraud,
Undue Influence, and Mistake, §§ 215.50-215.57, 215.141 (Matthew Bender)
9 California Points and Authorities, Ch. 92, Duress, Menace, Fraud, Undue
Influence, and Mistake, § 92.90 et seq. (Matthew Bender)
27 California Legal Forms, Ch. 77, Discharge of Obligations, § 77.350 (Matthew
Bender)
1 Matthew Bender Practice Guide: California Contract Litigation, Ch. 8, Seeking or
Opposing Equitable Remedies in Contract Actions, 8.24
1 Matthew Bender Practice Guide: California Contract Litigation, Ch. 16, Attacking
or Defending Existence of Contract - Mistake, 16.08[2], 16.13-16.16, 16.18
CONTRACTS CACI No. 330
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