Setting module property on Artifact causes warning message

Artifact {
    filePath: input.fileName
    fileTags: ["out"]
    qbs.install: true
    cpp.defines: ["X"]
}

Restoring build graph from disk
Resolving project for configuration default
WARNING: /home/kds/src/qbs_test/test.qbs:16:9 Item 'cpp' is not declared. Did you forget to add a Depends item?
WARNING: /home/kds/src/qbs_test/test.qbs:16:9 Item 'qbs' is not declared. Did you forget to add a Depends item?
Building for configuration default
Build done for configuration default.