diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index e74363f6aafca..9b29c643d8cf7 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -325,7 +325,8 @@ def write(string)
 
     # Allows you to manually set or override the response body.
     def body=(body)
-      if body.respond_to?(:to_path)
+      # Don't buffer things that shouldn't be buffered:
+      if body.respond_to?(:to_path) or !body.respond_to?(:to_ary)
         @stream = body
       else
         synchronize do