gistfile1.diff

diff --git a/lib/rspec/matchers/built_in/match_array.rb b/lib/rspec/matchers/built_in/match_array.rb
index f1ea560..671399c 100644
--- a/lib/rspec/matchers/built_in/match_array.rb
+++ b/lib/rspec/matchers/built_in/match_array.rb
@@ -2,8 +2,13 @@ module RSpec
   module Matchers
     module BuiltIn
       class MatchArray < BaseMatcher
+
+        def quacks_like_array?(object)
+          [:dup, :each, :index, :delete_at].map {|x| object.respond_to? x}.all?
+        end
+
         def match(expected, actual)
-          return false unless actual.is_a? Array
+          return false unless quacks_like_array? actual
 
           @extra_items = difference_between_arrays(actual, expected)
           @missing_items = difference_between_arrays(expected, actual)
@@ -11,7 +16,7 @@ module RSpec
         end
 
         def failure_message_for_should
-          if actual.is_a? Array
+          if quacks_like_array? actual
             message =  "expected collection contained:  #{safe_sort(expected).inspect}\n"
             message += "actual collection contained:    #{safe_sort(actual).inspect}\n"
             message += "the missing elements were:      #{safe_sort(@missing_items).inspect}\n" unless @missing_items.empty?