I am not quite sure what the best way to go. According to http://blogs.oracle.com/darcy/entry/bootclasspath_older_source the clean way to avoid this warning is to set the bootclasspath to the rt.jar (or equivalent) of the older platform. Another way to get rid of this warning is use a new sub option of -Xlint: -Xlint:-options. IMO Gradle should print this warning as it currently does and avoid any default bootclasspath and/or -Xlint values, which is intransparent for any user.