Automoc "No relevant classes found" for conditional Q_OBJECT in cpp

Building Qt Creator in release mode prints many warnings such as:

AutoMoc: src/plugins/qtsupport/qtparser.cpp: note: No relevant classes found. No output generated.

These files have Q_OBJECT inside #ifdef WITH_TESTS, so I guess automoc detects it as moc candidate, and moc warns because it finds no classes.

Is it possible to improve automoc to consider conditionals? If this is too hard, maybe you could add a flag for moc that suppresses this warning?