diff --git a/Doc/reference/index.rst b/Doc/reference/index.rst
index dff745c..bd1a281 100644
--- a/Doc/reference/index.rst
+++ b/Doc/reference/index.rst
@@ -18,6 +18,7 @@
 
 .. toctree::
    :maxdepth: 2
+   :numbered:
 
    introduction.rst
    lexical_analysis.rst