Type Error with Record.reduce on Schema Struct Object

This is probably such a noob question, but I have an object decoded from a Schema

Schema.Struct({ a: S.String.pipe(S.optional), b: S.String.pipe(S.optional) })

Schema.Struct({ a: S.String.pipe(S.optional), b: S.String.pipe(S.optional) })

that I want to

Record.reduce

Record.reduce

over, but I'm getting a type error that the input isn't a ReadonlyRecord, but 'just' a Record and I don't know how to narrow this?