diff --git a/setup.py b/setup.py
index 4bc5b0c..9cdb82d 100644
--- a/setup.py
+++ b/setup.py
@@ -26,5 +26,8 @@ setup(
         ]
     },
     install_requires=(),
+    extras_require = {
+        'multi_file': ['MarkdownPP'],
+    }
     include_package_data=True,
 )