diff --git a/doc/sphinx/conf.py.in b/doc/sphinx/conf.py.in
index 7b1115b9f57..3013dd1e135 100644
--- a/doc/sphinx/conf.py.in
+++ b/doc/sphinx/conf.py.in
@@ -118,7 +118,7 @@ todo_include_todos = True
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-#html_theme = 'classic'
+html_theme = 'classic'
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the