How to declare artiface for default configuration?

I have a project that builds an zip artifact using

task createPackage(type: Zip) {
    from "$buildDir/content"
artifacts {

Now I reference this project from another project using composite build. I get the error

Project : declares a dependency from configuration 'compile' to configuration 'default' which is not declared in the descriptor for project :project.

Before I was using a jar artifact (using java-library) instead of a zip artifact and it worked just fine.

How can I declare that the zip is the target for the default configuration?

Thanks a lot!