diff --git a/docs/conf.py b/docs/conf.py
index 0e8adfc31..ad1f73ed4 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -74,7 +74,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['sphinx.ext.autodoc','sphinx.ext.intersphinx','sphinx_design' ]
+extensions = ['sphinx.ext.autodoc','sphinx.ext.intersphinx','sphinx_design','sphinx_rtd_theme',]
 
 # To enable PDF generation, set METPLUS_DOC_PDF environment variable
 #  sphinx 2.4.2+ and rst2pdf packages are required