This is odd. The error indicates that there is a NsSet.class file in "/tmp/nsjava-0.0.9/java". This file shouldn't be there. Either there is a problem with how javac outputs the .class file on your system or you inadvertantly copied the NsSet.class file from the java/nsjava subdirectory into the java directory. Are there other .class files in the java directory? When I build on my machine, the only class file that exists in the java directory after building is the test_nsjvm.class file. The rest of the .class files should be in the nsjava subdirectory. If NsSet.class is the only .class file in the java directory, try removing it and running make again.