--- a/taskcluster/taskgraph/transforms/job/mozharness.py
+++ b/taskcluster/taskgraph/transforms/job/mozharness.py
@@ -170,21 +170,20 @@ def mozharness_on_docker_worker_setup(co
     command = [
         '/home/worker/bin/run-task',
         # Various caches/volumes are default owned by root:root.
         '--chown-recursive', '/home/worker/workspace',
         '--chown-recursive', '/home/worker/tooltool-cache',
         '--vcs-checkout', '/home/worker/workspace/build/src',
         '--tools-checkout', '/home/worker/workspace/build/tools',
         '--',
+        '/home/worker/workspace/build/src/{}'.format(
+            run.get('job-script', 'taskcluster/scripts/builder/build-linux.sh')
+        ),
     ]
-    command.append("/home/worker/workspace/build/src/{}".format(
-        run.get('job-script',
-                "taskcluster/scripts/builder/build-linux.sh"
-                )))
 
     worker['command'] = command
 
 
 @run_job_using("generic-worker", "mozharness", schema=mozharness_run_schema)
 def mozharness_on_generic_worker(config, job, taskdesc):
     assert job['worker']['os'] == 'windows', 'only supports windows right now'