diff --git a/doc/index.rst b/doc/index.rst
index b4174a72f..eadeacde2 100644
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -25,6 +25,7 @@ Contents
   Python package <python/index>
   R package <R-package/index>
   JVM package <jvm/index>
+  Ruby package <https://github.com/ankane/xgb>
   Julia package <julia>
   CLI interface <cli>
   contrib/index