diff --git a/actionpack/lib/action_controller/rack_process.rb b/actionpack/lib/action_controller/rack_process.rb
index 37b56dabca64925014d1ce39cf931e4433ab8e16..9b4aa9b7cfe0a5dcdde5a8768f14a8731eafc235 100644
--- a/actionpack/lib/action_controller/rack_process.rb
+++ b/actionpack/lib/action_controller/rack_process.rb
@@ -189,6 +189,8 @@ def each(&callback)
       if @body.respond_to?(:call)
         @writer = lambda { |x| callback.call(x) }
         @body.call(self, self)
+      elsif @body.is_a?(String)
+        @body.each_line(&callback)
       else
         @body.each(&callback)
       end