2 files changed, 6 insertions, 2 deletions
diff --git a/activesupport/lib/active_support/json/backends/jsongem.rb b/activesupport/lib/active_support/json/backends/jsongem.rb
index d1a1cdd7d7..649e6301d1 100644
--- a/activesupport/lib/active_support/json/backends/jsongem.rb
+++ b/activesupport/lib/active_support/json/backends/jsongem.rb
@@ -1,6 +1,8 @@
+require 'json' unless defined?(JSON)
+
 module ActiveSupport
   module JSON
-    ParseError = ::JSON::ParserError
+    ParseError = ::JSON::ParserError unless const_defined?(:ParseError)
 
     module Backends
       module JSONGem
diff --git a/activesupport/lib/active_support/json/backends/yaml.rb b/activesupport/lib/active_support/json/backends/yaml.rb
index 1c18fc4801..667016f45d 100644
--- a/activesupport/lib/active_support/json/backends/yaml.rb
+++ b/activesupport/lib/active_support/json/backends/yaml.rb
@@ -2,7 +2,9 @@ require 'active_support/core_ext/string/starts_ends_with'
 
 module ActiveSupport
   module JSON
-    class ParseError < StandardError
+    unless const_defined?(:ParseError)
+      class ParseError < StandardError
+      end
     end
 
     module Backends