diff --git a/setup.py b/setup.py
index aaa13de..bad634a 100644
--- a/setup.py
+++ b/setup.py
@@ -23,6 +23,7 @@
     'pyasn1-modules>=0.0.5',
     'rsa>=3.1.4',
     'six>=1.9.0',
+    'cachetools>=2.0.0',
 )