> For the complete documentation index, see [llms.txt](https://docs.aftermath.finance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aftermath.finance/perpetuals/architecture/self-trade-prevention.md).

# Self-Trade Prevention

When an incoming order would match against a resting order from the same address, the matching engine cancels the resting order instead of producing a fill. No fees are charged, and the cancellation does not appear in the trade feed.

On centralized exchanges, this behavior is commonly referred to as "expire maker." The resting (maker) order is expired so that the aggressing (taker) order can continue to fill against liquidity behind it, all the way up to its limit price.

### Why Expire Maker?

This is the preferred behavior for market-making algorithms. If your aggressing order matches against one of your own resting orders on the opposite side of the book, it means your resting order is stale. The engine removes it and lets the aggressing order continue through the book.


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