--- a/taskcluster/taskgraph/transforms/job/mozharness_test.py
+++ b/taskcluster/taskgraph/transforms/job/mozharness_test.py
@@ -443,16 +443,17 @@ def mozharness_test_on_script_engine_aut
         'MOZHARNESS_URL': {'task-reference': mozharness_url},
         'MOZILLA_BUILD_URL': {'task-reference': installer_url},
         "MOZ_NO_REMOTE": '1',
         "XPCOM_DEBUG_BREAK": 'warn',
         "NO_FAIL_ON_TEST_ERRORS": '1',
         "MOZ_HIDE_RESULTS_TABLE": '1',
         "MOZ_NODE_PATH": "/usr/local/bin/node",
         'MOZ_AUTOMATION': '1',
+        'WORKING_DIR': '/builds/worker',
         'WORKSPACE': '/builds/worker/workspace',
         'TASKCLUSTER_WORKER_TYPE': job['worker-type'],
     }
 
     # for fetch tasks on mobile
     if 'env' in job['worker'] and 'MOZ_FETCHES' in job['worker']['env']:
         env['MOZ_FETCHES'] = job['worker']['env']['MOZ_FETCHES']
         env['MOZ_FETCHES_DIR'] = job['worker']['env']['MOZ_FETCHES_DIR']