2 files changed, 1 insertions, 2 deletions
diff --git a/actionpack/lib/abstract_controller/rendering.rb b/actionpack/lib/abstract_controller/rendering.rb
index 6db0941b52..de00ffb0f9 100644
--- a/actionpack/lib/abstract_controller/rendering.rb
+++ b/actionpack/lib/abstract_controller/rendering.rb
@@ -107,7 +107,6 @@ module AbstractController
     end
 
     def _get_content_type(rendered_format) # :nodoc:
-      rendered_format.to_s
     end
 
     def _set_content_type(type) # :nodoc:
diff --git a/actionpack/lib/action_controller/metal/rendering.rb b/actionpack/lib/action_controller/metal/rendering.rb
index c8934b367f..363d45c722 100644
--- a/actionpack/lib/action_controller/metal/rendering.rb
+++ b/actionpack/lib/action_controller/metal/rendering.rb
@@ -57,7 +57,7 @@ module ActionController
     end
 
     def _get_content_type(rendered_format)
-      self.content_type || super
+      self.content_type || rendered_format.to_s
     end
 
     def _set_content_type(format)