diff --git a/README.md b/README.md
index 925b133..915789b 100644
--- a/README.md
+++ b/README.md
@@ -214,6 +214,8 @@ To install and use the `ykman` utility:
 ```console
 $ sudo apt -y install python-pip python-pyscard
 
+$ pip install PyOpenSSL
+
 $ pip install yubikey-manager
 
 $ sudo service pcscd start