diff --git a/test-requirements.txt b/test-requirements.txt
index a0842c55f..7dacdbe0d 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -6,7 +6,7 @@
 hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 coverage>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
-mock>=2.0 # BSD
+mock>=2.0,<4.0 # BSD
 python-subunit>=0.0.18 # Apache-2.0/BSD
 sphinx>=1.5.1,<2.0.0 # BSD
 sphinxcontrib-httpdomain # BSD