diff --git a/build/chromeos/PRESUBMIT.py b/build/chromeos/PRESUBMIT.py
index 312faf03ef537e..b4b3e2afb3c6ab 100644
--- a/build/chromeos/PRESUBMIT.py
+++ b/build/chromeos/PRESUBMIT.py
@@ -13,7 +13,11 @@ def CommonChecks(input_api, output_api):
   results += input_api.canned_checks.RunPylint(
       input_api, output_api, pylintrc='pylintrc')
   tests = input_api.canned_checks.GetUnitTestsInDirectory(
-      input_api, output_api, '.', [r'^.+_test\.py$'], run_on_python3=True)
+      input_api,
+      output_api,
+      '.', [r'^.+_test\.py$'],
+      run_on_python2=False,
+      run_on_python3=True)
   results += input_api.RunTests(tests)
   return results
 
diff --git a/build/chromeos/test_runner.py b/build/chromeos/test_runner.py
index c669e3565b096c..f859fa1dd8b20e 100755
--- a/build/chromeos/test_runner.py
+++ b/build/chromeos/test_runner.py
@@ -24,6 +24,8 @@
 import psutil  # pylint: disable=import-error
 import six
 
+assert not six.PY2, 'Use of this test runner with python 2 is not supported.'
+
 CHROMIUM_SRC_PATH = os.path.abspath(
     os.path.join(os.path.dirname(__file__), '..', '..'))