Java 8 default methods in interfaces and mixed groovy-java compilation

I’ve got some java code which contains the java8 interfaces with default methods.
I need to refer to it in my groovy code in the same sourceSet (main).

If I place the java code in the src/main/java tree, then the groovy code doesn’t compile because it can’t find the classes.
If I place the java code in the src/main/groovy tree, then the groovydoc task fails because it doesn’t know what to do with the default methods.

Is it possible to solve this problem?