diff --git a/activesupport/lib/active_support/xml_mini.rb b/activesupport/lib/active_support/xml_mini.rb
index 5cadcf634b..6e12404ad4 100644
--- a/activesupport/lib/active_support/xml_mini.rb
+++ b/activesupport/lib/active_support/xml_mini.rb
@@ -141,7 +141,7 @@ module ActiveSupport
     def _dasherize(key)
       # $2 must be a non-greedy regex for this to work
       left, middle, right = /\A(_*)(.*?)(_*)\Z/.match(key.strip)[1,3]
-      "#{left}#{middle.tr('_', '-')}#{right}"
+      "#{left}#{middle.tr('_ ', '--')}#{right}"
     end
 
 	  # TODO: Add support for other encodings