diff --git a/src/opserver/test-requirements.txt b/src/opserver/test-requirements.txt
index 32bc39eaa02..93b1843dd12 100644
--- a/src/opserver/test-requirements.txt
+++ b/src/opserver/test-requirements.txt
@@ -10,6 +10,7 @@ flexmock==0.9.7
 kafka-python==0.9.2
 kazoo
 stevedore
+Cython==0.24.1
 cassandra-driver==3.0.0
 ../../../controller/src/analytics/test/utils/mockredis
 ../../../controller/src/analytics/test/utils/mockcassandra