How do I constrain associated types on a non-owned trait?

Question

Here is a link to this example in Rust playground

I am creating two traits. The one trait uses the other as an associated type. The associated trait extends FromStr:

trait Behaviour where Self: FromStr {}
trait AnotherBehaviour {
    type Assoc: Behaviour;
}

I can implement these traits for Derp and AnotherDerp respectively, remembering to implement FromStr for Derp:

struct Error {}
struct Derp {}
struct AnotherDerp {}

impl Behaviour for Derp {}
impl FromStr for Derp {
    type Err = Error;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s { "derp" => Ok(Derp{}), _ => Err(Error {}) }
    }
}

impl AnotherBehaviour for AnotherDerp {
    type Assoc = Derp;
}

Now I want to create a generic function that uses the encapsulating trait.

fn run<T: AnotherBehaviour>() {
    let derp = T::Assoc::from_str("derp").expect("expected derp");
}

fn main() {
    run::<AnotherDerp>();
}

I get the error:

note: the method `expect` exists but the following trait bounds were not satisfied:
       `<<T as AnotherBehaviour>::Assoc as std::str::FromStr>::Err : std::fmt::Debug`

I implement Debug for my Error type:

#[derive(Debug)]
struct Error {}

But this won't work because I actually need to constrain the trait.

I know that I can constrain the generic function with

where
    <T::Assoc as FromStr>::Err: Debug,

but how can I constrain the Behaviour or AnotherBehaviour trait to require FromStr::Err to implement Debug? I can't figure out the syntax.

I have tried

trait Behaviour: FromStr
where
     <Self as FromStr>::Err: Debug

and

trait Behaviour: FromStr
where
    Self::Err: Debug