error[E0599]: no method named `foo` found for reference `&dyn Foo` in the current scope --> $DIR/issue-5153.rs:10:27 | LL | fn foo(self: Box); | --------- the method might not be found because of this arbitrary self type ... LL | (&5isize as &dyn Foo).foo(); | ^^^ method not found in `&dyn Foo` error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0599`.