diff --git a/doc/manual/conf.py b/doc/manual/conf.py
index d53d3bc56..072c2a717 100644
--- a/doc/manual/conf.py
+++ b/doc/manual/conf.py
@@ -51,6 +51,7 @@ from artiq import __version__ as artiq_version
 extensions = [
     'sphinx.ext.autodoc',
     'sphinx.ext.mathjax',
+    'sphinx.ext.viewcode',
     'sphinxarg.ext',
 ]