Thanks to Maurizio for reporting this:

// -- X.java
sealed interface Foo permits Bar { }
primitive class Bar implements Foo { }

class Test {
   void test(Object o) {
      Foo foo = (Foo)o;
   }
}
$javac -g X.java
X.java:6: error: incompatible types: Object cannot be converted to Foo
      Foo foo = (Foo)o;
                     ^
1 error


Error goes away if interface is not sealed.