diff --git a/api/controller/controller_util.py b/api/controller/controller_util.py
index ba4031b..3b1bf52 100644
--- a/api/controller/controller_util.py
+++ b/api/controller/controller_util.py
@@ -7,6 +7,8 @@
 
 from __future__ import print_function
 
+import sys
+
 from chromite.api.gen.chromiumos import common_pb2
 from chromite.cbuildbot import goma_util
 from chromite.lib import constants
@@ -15,6 +17,9 @@
 from chromite.lib.chroot_lib import Chroot
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 class Error(Exception):
   """Base error class for the module."""