diff --git a/src/class.c b/src/class.c
index 043b5e3c0..69aa31249 100644
--- a/src/class.c
+++ b/src/class.c
@@ -809,6 +809,34 @@ mrb_mod_included_modules(mrb_state *mrb, mrb_value self)
 
 mrb_value class_instance_method_list(mrb_state*, int, mrb_value*, struct RClass*, int);
 
+/* 15.2.2.4.33 */
+/*
+ *  call-seq:
+ *     mod.instance_methods(include_super=true)   -> array
+ *
+ *  Returns an array containing the names of the public and protected instance
+ *  methods in the receiver. For a module, these are the public and protected methods;
+ *  for a class, they are the instance (not singleton) methods. With no
+ *  argument, or with an argument that is <code>false</code>, the
+ *  instance methods in <i>mod</i> are returned, otherwise the methods
+ *  in <i>mod</i> and <i>mod</i>'s superclasses are returned.
+ *
+ *     module A
+ *       def method1()  end
+ *     end
+ *     class B
+ *       def method2()  end
+ *     end
+ *     class C < B
+ *       def method3()  end
+ *     end
+ *
+ *     A.instance_methods                #=> [:method1]
+ *     B.instance_methods(false)         #=> [:method2]
+ *     C.instance_methods(false)         #=> [:method3]
+ *     C.instance_methods(true).length   #=> 43
+ */
+
 static mrb_value
 mrb_mod_instance_methods(mrb_state *mrb, mrb_value mod)
 {