❤ 1.9

activesupport/lib/active_support/inflector/methods.rb

@@ -91,7 +91,7 @@ def camelize(term, uppercase_first_letter = true)
     def underscore(camel_cased_word)
       return camel_cased_word unless camel_cased_word =~ /[A-Z-]|::/
       word = camel_cased_word.to_s.gsub('::', '/')
-      word.gsub!(/(?<=([A-Za-z\d])|\b)(#{inflections.acronym_regex})(?=\b|[^a-z])/) { "#{$1 && '_'}#{$2.downcase}" }
+      word.gsub!(/(?:(?<=([A-Za-z\d]))|\b)(#{inflections.acronym_regex})(?=\b|[^a-z])/) { "#{$1 && '_'}#{$2.downcase}" }
       word.gsub!(/([A-Z\d]+)([A-Z][a-z])/,'\1_\2')
       word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')
       word.tr!("-", "_")