How to use java classes of DC1 in DC2

When I was trying to use a java-class from another DC, I stumbled into an error I didn't expect:

java.lang.NoClassDefFoundError: com/company/application/utils

This is what I did to get this far:

1. Created an empty Web Dynpro DC (DC1), to be used as a utilities library.

2. Added a Java class to the webdynpro project.

3. Added the class to a public part of type compilation.

4. Created a second Web Dynpro DC (DC2), which is supposed to consume the class from DC1.

5. Added a DC-usage relation, so that DC1 is in DC2's used DCs. In this usage-relation built-time and run-time were checked

5. Used DC1's class in DC2's component controller

6. Built both DCs and deployed them

7. Ran the application in DC2.

When I run the application, the application dumps a stack trace at the moment that and object is created based on the class in DC1.

Any idea how to get this working?