diff --git a/actionpack/lib/action_dispatch/middleware/show_exceptions.rb b/actionpack/lib/action_dispatch/middleware/show_exceptions.rb
index 0a6d2bfc8a112..e095b51342427 100644
--- a/actionpack/lib/action_dispatch/middleware/show_exceptions.rb
+++ b/actionpack/lib/action_dispatch/middleware/show_exceptions.rb
@@ -122,7 +122,7 @@ def status_code(exception)
       end
 
       def render(status, body)
-        [status, {'Content-Type' => 'text/html', 'Content-Length' => body.length.to_s}, [body]]
+        [status, {'Content-Type' => 'text/html', 'Content-Length' => body.bytesize.to_s}, [body]]
       end
 
       def public_path