diff --git a/requirements_dev.txt b/requirements_dev.txt
index c7984aa..edb55c4 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -21,4 +21,4 @@ flake8==3.4.1
 coverage==4.4.1
 Sphinx==1.6.3
 sphinxcontrib-napoleon==0.6.1
-cryptography==2.6.1
+cryptography==3.1