diff --git a/lower-constraints.txt b/lower-constraints.txt
index a442ffc..c874f08 100644
--- a/lower-constraints.txt
+++ b/lower-constraints.txt
@@ -26,6 +26,7 @@
 linecache2==1.0.0
 MarkupSafe==1.0
 mccabe==0.2.1
+mock==2.0.0
 monotonic==1.4
 mox3==0.25.0
 msgpack==0.5.6