diff --git a/lib/spack/docs/conf.py b/lib/spack/docs/conf.py
index 76ff0f921b6..35637093da9 100644
--- a/lib/spack/docs/conf.py
+++ b/lib/spack/docs/conf.py
@@ -134,6 +134,7 @@
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.graphviz',
+              'sphinx.ext.napoleon',
               'sphinx.ext.todo',
               'sphinxcontrib.programoutput']