diff --git a/tools/download_file.py b/tools/download_file.py
index 90222c68..901387d2 100755
--- a/tools/download_file.py
+++ b/tools/download_file.py
@@ -7,6 +7,7 @@ from __future__ import print_function
 import argparse
 import os
 import sys
+import time
 
 try:
     from urllib2 import HTTPError, URLError, urlopen