diff --git a/readthedocs-pip-requirements.txt b/readthedocs-pip-requirements.txt
index 47c468b..061e669 100644
--- a/readthedocs-pip-requirements.txt
+++ b/readthedocs-pip-requirements.txt
@@ -1,2 +1,3 @@
 numpydoc==0.4
 contextlib2==0.4.0
+mock==1.0.1