diff --git a/utils/libcxx/util.py b/utils/libcxx/util.py
index 389fc32aa..ecfb9afb7 100644
--- a/utils/libcxx/util.py
+++ b/utils/libcxx/util.py
@@ -8,13 +8,14 @@
 #===----------------------------------------------------------------------===##
 
 from contextlib import contextmanager
+import errno
 import os
 import platform
 import signal
 import subprocess
 import sys
 import tempfile
-
+import threading
 
 
 # FIXME: Most of these functions are cribbed from LIT