---
title: "Announcing User Defined Type Guards in Flow"
short-title: "Announcing User Defined Type Guards in Flow"
author: "Panagiotis Vekris"
medium-link: "https://medium.com/flow-type/announcing-user-defined-type-guards-in-flow-b979bb2e78cf"
---
Flow now lets you define a function that encodes a type predicate over its parameter.
