Concrete source from error

I have an instance of type MyError which implements std::error::Error and overrides the default fn source.

How, would I go about using that to get a reference to the concrete type that was used when making the instance of MyError?

I have the following snippet:

let e: MyError = ...;
if let Some(s) = e.source() {
    if let Some(s_err) = s.as_any().downcast_ref::<SourceErr>() {
        ...
    }
}

But the compiler complains that no method as_any exists for &dyn std:error::Error. I have tried looking for another solution to this but I have failed to.

https://doc.rust-lang.org/std/error/trait.Error.html#method.downcast_ref