diff --git a/docs/conf.py b/docs/conf.py
index 8fb53e890c..b06ee8a8a5 100755
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -246,6 +246,8 @@ latex_elements = {
 
 # Additional stuff for the LaTeX preamble.
 #'preamble': '',
+# Include 3 levels of headers in PDF ToC
+'preamble': '\setcounter{tocdepth}{2}',
 }
 
 # Grouping the document tree into LaTeX files. List of tuples