diff --git a/book/source/conf.py b/book/source/conf.py
index 9d8cf4e..fcd2ad5 100644
--- a/book/source/conf.py
+++ b/book/source/conf.py
@@ -8,6 +8,7 @@
 
 project = 'OpenPGP for application developers'
 copyright = '2023, The "Notes on OpenPGP" project'
+version = "0.01"
 
 # -- General configuration ---------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration