diff --git a/Doc/conf.py b/Doc/conf.py
index 0cfbea6..2be0f19 100644
--- a/Doc/conf.py
+++ b/Doc/conf.py
@@ -63,6 +63,9 @@
 # unit titles (such as .. function::).
 add_module_names = True
 
+# By default, highlight as Python 3.
+highlight_language = 'python3'
+
 
 # Options for HTML output
 # -----------------------