diff --git a/requirements.txt b/requirements.txt
index 2bc1a99237..4b56d265cc 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,5 +7,5 @@ setuptools
 #
 pyserial>=3.0
 future>=0.15.2
-cryptography>=2.1.4
+cryptography>=2.1.4,<35
 pyparsing>=2.0.3,<2.4.0