From cad635995ca945d4137d0aab64d46313aee4f556 Mon Sep 17 00:00:00 2001
From: Matthew Draper <matthew@trebex.net>
Date: Sat, 4 Oct 2014 08:41:03 +0930
Subject: :heart: 1.9

---
 activesupport/lib/active_support/inflector/methods.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/activesupport/lib/active_support/inflector/methods.rb b/activesupport/lib/active_support/inflector/methods.rb
index 5b75dd65d0..0e3c8517d1 100644
--- a/activesupport/lib/active_support/inflector/methods.rb
+++ b/activesupport/lib/active_support/inflector/methods.rb
@@ -91,7 +91,7 @@ module ActiveSupport
     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!("-", "_")
-- 
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