diff --git a/ext/json/lib/json/common.rb b/ext/json/lib/json/common.rb
index b5fbfcf05d..254ed0920b 100644
--- a/ext/json/lib/json/common.rb
+++ b/ext/json/lib/json/common.rb
@@ -236,10 +236,6 @@ module JSON
   # deep.
   class NestingError < ParserError; end
 
-  # :stopdoc:
-  class CircularDatastructure < NestingError; end
-  # :startdoc:
-
   # This exception is raised if a generator or unparser error occurs.
   class GeneratorError < JSONError
     attr_reader :invalid_object