diff --git a/requirements/core.txt b/requirements/core.txt
index 24cad8d3e..1e1d0a8dd 100644
--- a/requirements/core.txt
+++ b/requirements/core.txt
@@ -2,3 +2,4 @@ jsonschema==3.2.0
 pyrsistent==0.14.0
 mmh3==2.5.1
 requests[security]>=2.9.1
+cryptography>=1.3.4,<=3.1.1