---
title: Exceptional ERC20s
---

Some ERC20s have unique behavior that may require extra handling. We
document these here as they are discovered.

# Assert vs Require

These ERC20\'s use [assert]{.title-ref} instead of
[require]{.title-ref}, which means that if the token reverts then
(nearly) all of the gas from your transaction will be consumed.
Specifically, you are left with 1/64 of the gas limit. Be mindful of
this when implementing fallback logic; for example, if a call to
[transferFrom]{.title-ref} reverts then note you will only have 1/64 of
the gas limit to handle the exception.

Known tokens:

-   KNC
-   LINK
-   sUSD
-   USDT