# X_SCHEMA_DISCRIMINANT_INVALID

## Means

a discriminated union member can never be dispatched to

## Typical cause

a member of `t.discriminatedUnion('<key>', […])` that declares no literal at the discriminant, or one whose tag an earlier member already claims. Thrown where the union is **built**, not where a value is parsed: a member no tag routes to is wrong for every input, so the first import of the authoring file is the earliest honest place to say so

## Fix

give the member named in `cause` a literal discriminant — `t.object({ <key>: t.literal('…'), … })` — its own value at that key, or merge the two members into one; `t.union(...)` if the members share no key

[Schema and validation](/error-codes#schema-and-validation)