Non-Standard ERC-20 Token
Abbreviation: ERC-20
Pronunciation: non-STAN-derd E-R-C TWEN-tee TOH-kun
Also known as: Non-Compliant ERC-20 Token, ERC-20-Compatible Token with Deviations, ERC-20
Definition
A non-standard ERC-20 token is a token that resembles or claims compatibility with ERC-20 but deviates from expected interface or behavioral conventions. Examples include missing return values, transfer fees, rebasing balances, pausing, blacklisting, unusual decimals, or transfer restrictions. Such tokens may work in some wallets while breaking generic integrations.
Overview
Meaning and scope
A non-standard ERC-20 token is a token that resembles or claims compatibility with ERC-20 but deviates from expected interface or behavioral conventions. Examples include missing return values, transfer fees, rebasing balances, pausing, blacklisting, unusual decimals, or transfer restrictions. Such tokens may work in some wallets while breaking generic integrations.
Mechanism and operation
Wrappers and libraries often add compatibility logic, but an integration that makes strict assumptions can fail, lock funds, or incorrectly mark a payment as complete. Behavioral extensions can also make a token operationally non-standard. Fee-on-transfer tokens deliver less than the requested amount; rebasing tokens change balances without transfers; blacklistable tokens can freeze addresses; and tokens with hooks or upgradeable logic may introduce additional execution paths. Unusual decimal values and non-standard approval behavior can cause amount and allowance errors even when the function signatures appear familiar. Payment processors should maintain an allowlist and perform contract-specific tests for transfer amount, event emission, return data, fee deductions, and administrative controls.
Practical payment example
A token deducts fees during transfer, so a gateway receives less than the nominal amount and must reconcile actual on-chain balance changes.
Operational checks
The received balance, not only the transaction input, should be reconciled. Refund and payout logic must account for tokens that charge fees or restrict recipients. Static interface detection is not enough because a contract can implement standard selectors while violating expected semantics. The label “non-standard” does not necessarily mean malicious or unusable.
Distinctions and limits
ERC-20 defines a common interface for token balances, transfers, allowances, and events, but deployed contracts do not always follow it exactly. Some older tokens omit the Boolean return value from transfer functions, while others revert or return false under different conditions.
Related reading
Related definitions: verified contract address, market and redemption value.
Example
A token deducts fees during transfer, so a gateway receives less than the nominal amount and must reconcile actual on-chain balance changes.
Comparison
ERC-20 defines a common interface for token balances, transfers, allowances, and events, but deployed contracts do not always follow it exactly. Some older tokens omit the Boolean return value from transfer functions, while others revert or return false under different conditions.
Key Takeaway
A non-standard ERC-20 token may expose familiar functions while violating expected behavior, so integrations must test the contract rather than trust the label.
Sources
- ERC-20: Token Standard — Ethereum Improvement Proposals (2026-08-02)
- Issues, Risks and Regulatory Considerations Relating to Crypto-Asset Trading Platforms — International Organization of Securities Commissions (2026-08-02)
- Taxonomy of Legal Issues Related to the Digital Economy — UNCITRAL (2026-08-02)