diff --git a/actionpack/lib/action_controller/request.rb b/actionpack/lib/action_controller/request.rb
index 214edf250e11d3963e0290837a00b667094bb2d5..af81f0775ae1650e3fed539b436b3e55b14f7312 100755
--- a/actionpack/lib/action_controller/request.rb
+++ b/actionpack/lib/action_controller/request.rb
@@ -35,7 +35,7 @@ def post_format
       if env['HTTP_X_POST_DATA_FORMAT']
         env['HTTP_X_POST_DATA_FORMAT'].downcase.intern
       else
-        case env['HTTP_CONTENT_TYPE']
+        case env['CONTENT_TYPE']
           when 'application/xml', 'text/xml'
             :xml
           when 'application/x-yaml', 'text/x-yaml'