1 files changed, 7 insertions, 2 deletions
diff --git a/activesupport/lib/active_support/json/backends/yaml.rb b/activesupport/lib/active_support/json/backends/yaml.rb
index c7db508c23..667016f45d 100644
--- a/activesupport/lib/active_support/json/backends/yaml.rb
+++ b/activesupport/lib/active_support/json/backends/yaml.rb
@@ -2,15 +2,20 @@ 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
       module Yaml
         extend self
 
-        # Converts a JSON string into a Ruby object.
+        # Parses a JSON string or IO and converts it into an object
         def decode(json)
+          if json.respond_to?(:read)
+            json = json.read
+          end
           YAML.load(convert_json_to_yaml(json))
         rescue ArgumentError => e
           raise ParseError, "Invalid JSON string"