# 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. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.aftermath.finance/perpetuals/architecture/self-trade-prevention.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.