diff --git a/tests/test_momo.py b/tests/test_momo.py
index cab3a7d6..9ff98eec 100644
--- a/tests/test_momo.py
+++ b/tests/test_momo.py
@@ -27,7 +27,7 @@ class MomoEnabled(object):
 def assets_base():
     assets_base_path = os.path.join(settings.MEDIA_ROOT, 'assets-base.zip')
     if not os.path.exists(assets_base_path):
-        fd = open(assets_base_path, 'w')
+        fd = open(assets_base_path, 'wb')
         z = zipfile.ZipFile(fd, 'w')
         z.close()