# X_ERROR_DECLARATION_INVALID

## Means

a defineError declaration is malformed

## Typical cause

`defineError()` given both or neither of `status` and `offSocket`, a status outside 100-599, or a code that is not `X_` followed by SCREAMING_SNAKE words

## Fix

`edit the defineError call the cause names, then x verify --only errors`

[Core and runtime](/error-codes#core-and-runtime)