diff --git a/src/doc/conf.py b/src/doc/conf.py
index 62a8cbb9c9d5ca80a35e3aa686d1b6c4d29b8bb6..a25566a27aaf861d571250ae3c14783051d8db3b 100644
--- a/src/doc/conf.py
+++ b/src/doc/conf.py
@@ -52,7 +52,11 @@ templates_path = ['_templates']
 # You can specify multiple suffix as a list of string:
 #
 # source_suffix = ['.rst', '.md']
-source_suffix = '.rst'
+source_suffix = {
+    '.rst': 'restructuredtext',
+    '.md': 'markdown',
+}
+
 
 # The master toctree document.
 master_doc = 'index'