Confusing parse error with let bindings

This code:
```rust
fn main() {
    let a = 3
}
```
gives the error:
```
error: expected one of `.`, `;`, `?`, or an operator, found `}`
 --> src/main.rs:3:1
  |
2 |     let a = 3
  |              - expected one of `.`, `;`, `?`, or an operator here
3 | }
  | ^ unexpected token
```

It would be nice if this would instead say that `let` is not an expression.