diff --git a/activesupport/lib/active_support/ordered_options.rb b/activesupport/lib/active_support/ordered_options.rb
index ea822706e85e6fecd38edf6a277d2d9c5dd2d1d7..6ba1346c79b2415ccf94eed980cacf24f470b18d 100644
--- a/activesupport/lib/active_support/ordered_options.rb
+++ b/activesupport/lib/active_support/ordered_options.rb
@@ -39,7 +39,7 @@ def [](key)
     end
 
     def method_missing(name, *args)
-      name_string = +name.to_s
+      name_string = name.to_s.dup
       if name_string.chomp!("=")
         self[name_string] = args.first
       else