1 files changed, 16 insertions, 1 deletions
diff --git a/activesupport/lib/active_support/json/decoding.rb b/activesupport/lib/active_support/json/decoding.rb
index a5908365af..e357b6837a 100644
--- a/activesupport/lib/active_support/json/decoding.rb
+++ b/activesupport/lib/active_support/json/decoding.rb
@@ -6,12 +6,15 @@ module ActiveSupport
   mattr_accessor :parse_json_times
 
   module JSON
+    # Listed in order of preference.
+    DECODERS = %w(Yajl JSONGem Yaml)
+
     class << self
       attr_reader :parse_error
       delegate :decode, :to => :backend
 
       def backend
-        self.backend = "Yaml" unless defined?(@backend)
+        set_default_backend unless defined?(@backend)
         @backend
       end
 
@@ -31,6 +34,18 @@ module ActiveSupport
       ensure
         self.backend = old_backend
       end
+
+      def set_default_backend
+        DECODERS.find do |name|
+          begin
+            self.backend = name
+            true
+          rescue LoadError
+            # Try next decoder.
+            false
+          end
+        end
+      end
     end
   end
 end