1 files changed, 4 insertions, 3 deletions
diff --git a/activesupport/lib/active_support/json/encoding.rb b/activesupport/lib/active_support/json/encoding.rb
index 42a217cedc..acccb62aea 100644
--- a/activesupport/lib/active_support/json/encoding.rb
+++ b/activesupport/lib/active_support/json/encoding.rb
@@ -4,10 +4,11 @@ module ActiveSupport
     end
 
     # Converts a Ruby object into a JSON string.
-    def self.encode(value, options = {})
+    def self.encode(value, options = nil)
+      options ||= {}
       seen = (options[:seen] ||= [])
-      raise CircularReferenceError, 'object references itself' if seen.include?(value)
-      seen << value
+      raise CircularReferenceError, 'object references itself' if seen.include?(value.object_id)
+      seen << value.object_id
       value.send(:rails_to_json, options)
     ensure
       seen.pop