diff --git a/cibuildwheel/macos.py b/cibuildwheel/macos.py
index bc9fe388..75d0d4ae 100644
--- a/cibuildwheel/macos.py
+++ b/cibuildwheel/macos.py
@@ -1,5 +1,5 @@
 from __future__ import print_function
-import os, subprocess, shlex
+import os, subprocess, shlex, sys
 from collections import namedtuple
 from glob import glob
 try:
diff --git a/cibuildwheel/windows.py b/cibuildwheel/windows.py
index 173ffc21..daf746e6 100644
--- a/cibuildwheel/windows.py
+++ b/cibuildwheel/windows.py
@@ -1,5 +1,5 @@
 from __future__ import print_function
-import os, tempfile, subprocess, urllib2
+import os, tempfile, subprocess, urllib2, sys
 from collections import namedtuple
 
 from .util import prepare_command