diff --git a/book/source/conf.py b/book/source/conf.py
index fcd2ad5..80f4181 100644
--- a/book/source/conf.py
+++ b/book/source/conf.py
@@ -28,3 +28,8 @@ exclude_patterns = []
 
 html_theme = 'alabaster'
 html_static_path = ['_static']
+
+# https://github.com/sphinx-doc/alabaster/blob/0.x/alabaster/theme.conf
+html_theme_options = {
+    'code_font_size': '9pt',
+}