diff --git a/python/mozbuild/mozbuild/util.py b/python/mozbuild/mozbuild/util.py
--- a/python/mozbuild/mozbuild/util.py
+++ b/python/mozbuild/mozbuild/util.py
@@ -2,10 +2,11 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this file,
 # You can obtain one at http://mozilla.org/MPL/2.0/.
 
 # This file contains miscellaneous utility functions that don't belong anywhere
 # in particular.
+import enum
 import argparse
 import collections
 import collections.abc
 import copy
 import difflib