diff --git a/scripts/combo-layer b/scripts/combo-layer
index 0644cdc073..0954bb6850 100755
--- a/scripts/combo-layer
+++ b/scripts/combo-layer
@@ -33,6 +33,7 @@ import pipes
 import shutil
 from collections import OrderedDict
 from string import Template
+from functools import reduce
 
 __version__ = "0.2.1"