diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 07c2bcf0..d73e0714 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -4363,7 +4363,20 @@ BigDecimal_negative_zero(void)
  *      (2/3r).to_d(3)  # => 0.667e0
  *      "0.5".to_d      # => 0.5e0
  *
- * == License
+ * == Methods for Working with \JSON
+ *
+ * - {::json_create}[https://docs.ruby-lang.org/en/master/BigDecimal.html#method-c-json_create]:
+ *   Returns a new \BigDecimal object constructed from the given object.
+ * - {#as_json}[https://docs.ruby-lang.org/en/master/BigDecimal.html#method-i-as_json]:
+ *   Returns a 2-element hash representing +self+.
+ * - {#to_json}[https://docs.ruby-lang.org/en/master/BigDecimal.html#method-i-to_json]:
+ *   Returns a \JSON string representing +self+.
+ *
+ * To make these methods available:
+ *
+ *   require 'json/add/bigdecimal'
+ *
+ * * == License
  *
  * Copyright (C) 2002 by Shigeo Kobayashi <shigeo@tinyforest.gr.jp>.
  *