1 files changed, 7 insertions, 5 deletions
diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index c7df62e915..b3dc5b2f3a 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -36,11 +36,13 @@ module ActiveSupport
     #   "ActiveRecord".underscore         # => "active_record"
     #   "ActiveRecord::Errors".underscore # => active_record/errors
     def underscore(camel_cased_word)
-      camel_cased_word.to_s.gsub(/::/, '/').
-        gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
-        gsub(/([a-z\d])([A-Z])/,'\1_\2').
-        tr("-", "_").
-        downcase
+      word = camel_cased_word.to_s.dup
+      word.gsub!(/::/, '/')
+      word.gsub!(/([A-Z]+)([A-Z][a-z])/,'\1_\2')
+      word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')
+      word.tr!("-", "_")
+      word.downcase!
+      word
     end
 
     # Replaces underscores with dashes in the string.