`from_read` issue constructing a generic `Deserializer`

I am trying to construct a `Deserializer` for use with `serde_transcode`, but it is failing:

```rust
let mut deserializer: rmp_serde::Deserializer<_> = rmp_serde::from_read(input).unwrap();
```

`input` has the type `Box`. The converse does seem to work:

```rust
let mut serializer = rmp_serde::Serializer::new(output);
```

What is the correct construction?