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Standards Track: Core

EIP-684: Revert creation in case of collision

Revert contract creation if address already has code

Authors Vitalik Buterin (@vbuterin), Renan Rodrigues de Souza (@RenanSouza2)
Created 2023-03-20


This EIP causes contract creation to throw an error when attempted at an address with pre-existing code. This prevents an attack consisting of deploying contract code and later changing the code arbitrarily by “creating” an account at that existing address.


The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119 and RFC 8174.

If a contract creation is attempted due to a creation transaction, the CREATE opcode, the CREATE2 opcode, or any other reason, and the destination address already has either a nonzero nonce, or a nonzero code length, then the creation MUST throw as if the first byte in the init code were an invalid opcode. This change MUST apply retroactively for all existing blocks.


One of the core tenants of smart contracts is that its code will not change. However with sufficient computing power an attacker can change the code stored in an address to any other code, steal funds or execute other malicious activity.

Backwards Compatibility

This is an execution layer upgrade, and so it requires a hard fork.

Test Cases

Given a genesis allocation of

Address : 0xd0bBEc6D2c628b7e2E6D5556daA14a5181b604C5,
Balance : 1000000000000000000, // 1 ether
Nonce   : 0,
code    : "",

Address : 0x7658771dc6Af74a3d2F8499D349FF9c1a0DF8826,
Balance : 0,
Nonce   : 1,
Code    : "0xB0B0FACE",

A contract created in the first transaction from EOA 0xd0bBEc6... (227bcc6959669226360814723ed739f1214201584b6a27409dfb8228b8be5f59), with no salt, should revert.

Security Considerations

This EIP is a security upgrade: it enforces the imutability of deployed code.

Copyright and related rights waived via CC0.


Please cite this document as:

Vitalik Buterin (@vbuterin), Renan Rodrigues de Souza (@RenanSouza2), "EIP-684: Revert creation in case of collision," Ethereum Improvement Proposals, no. 684, March 2023. [Online serial]. Available: