diff --git a/mrbgems/mruby-toplevel-ext/mrblib/toplevel.rb b/mrbgems/mruby-toplevel-ext/mrblib/toplevel.rb
index e5fc6239f..688d78afe 100644
--- a/mrbgems/mruby-toplevel-ext/mrblib/toplevel.rb
+++ b/mrbgems/mruby-toplevel-ext/mrblib/toplevel.rb
@@ -1,6 +1,23 @@
 class <<self
   private
 
+  #
+  # call-seq:
+  #   include(module, ...) -> self
+  #
+  # Invokes Module.append_features on each parameter in reverse order.
+  # When called at the toplevel, this includes the module(s) into Object,
+  # making their methods available to all objects.
+  #
+  #   module Greeting
+  #     def hello
+  #       "Hello, world!"
+  #     end
+  #   end
+  #
+  #   include Greeting
+  #   "".hello  #=> "Hello, world!"
+  #
   def include(*modules)
     Object.include(*modules)
   end