---
title: "Announcing User Defined Type Guards in Flow"
short-title: "Announcing User Defined Type Guards in Flow"
authors: [panagiotis-vekris]
medium-link: "https://medium.com/flow-type/announcing-user-defined-type-guards-in-flow-b979bb2e78cf"
---

:::info[Historical]
This post announced user-defined type guards when it was introduced. For current syntax and behavior, see the [Type Guards](/en/docs/types/type-guards) documentation.
:::

Flow now lets you define a function that encodes a type predicate over its parameter.

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