diff --git a/lower-constraints.txt b/lower-constraints.txt
index bddc7c4d..c2f98ef4 100644
--- a/lower-constraints.txt
+++ b/lower-constraints.txt
@@ -32,7 +32,7 @@ linecache2==1.0.0
 Mako==0.4.0
 MarkupSafe==1.0
 mccabe==0.2.1
-mock==2.0.0
+mock==4.0.3
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0