diff --git a/Gemfile b/Gemfile
index 697b11a..da9c0df 100644
--- a/Gemfile
+++ b/Gemfile
@@ -6,6 +6,7 @@ group :development, :test do
   gem 'simplecov-lcov', '~> 0.8',  platforms: :mri
   gem 'benchmark-ips'
   gem 'rake'
+  gem 'activesupport'
 end
 
 group :debug do
diff --git a/lib/json/canonicalization.rb b/lib/json/canonicalization.rb
index e972eaf..e8ec97f 100644
--- a/lib/json/canonicalization.rb
+++ b/lib/json/canonicalization.rb
@@ -15,7 +15,7 @@ class Object
   # Default canonicalization output for Ruby objects
   # @return [String]
   def to_json_c14n
-    self.to_json
+    ::JSON.generate(self)
   end
 end
 
@@ -86,7 +86,7 @@ class String
   # Output JSON with control characters escaped
   # @return [String]
   def to_json_c14n
-    self.to_json
+    ::JSON.generate(self)
   end
 end
 
@@ -94,7 +94,6 @@ class Symbol
   # Output JSON with control characters escaped
   # @return [String]
   def to_json_c14n
-    self.to_json
+    ::JSON.generate(self)
   end
 end
-
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index bbd5c8e..2e8a590 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -2,6 +2,8 @@
 
 require "bundler/setup"
 require 'rspec'
+require 'active_support'
+require 'active_support/core_ext'
 
 begin
   require 'simplecov'