--- a/taskcluster/taskgraph/transforms/upload_generated_sources.py
+++ b/taskcluster/taskgraph/transforms/upload_generated_sources.py
@@ -29,15 +29,17 @@ def add_task_info(config, jobs):
         # Copy over some bits of metdata from the build task.
         dep_th = dep_task.task['extra']['treeherder']
         job.setdefault('attributes', {})
         job['attributes']['build_platform'] = dep_task.attributes.get('build_platform')
         plat = '{}/{}'.format(dep_th['machine']['platform'], dep_task.attributes.get('build_type'))
         job['treeherder']['platform'] = plat
         job['treeherder']['tier'] = dep_th['tier']
         # Add an environment variable pointing at the artifact from the build.
+        # XXX This will break with any non-public artifact_prefix, but I believe
+        # these tasks are going away with buildbot.
         artifact_url = get_artifact_url('<build>',
                                         'public/build/target.generated-files.tar.gz')
         job['worker'].setdefault('env', {})['ARTIFACT_URL'] = {
             'task-reference': artifact_url
         }
 
         yield job