diff --git a/lib/aws-missing-tools/aws-ha-release/aws-ha-release.rb b/lib/aws-missing-tools/aws-ha-release/aws-ha-release.rb
index cc48c64..b612984 100755
--- a/lib/aws-missing-tools/aws-ha-release/aws-ha-release.rb
+++ b/lib/aws-missing-tools/aws-ha-release/aws-ha-release.rb
@@ -98,7 +98,7 @@ module AwsMissingTools
       @group.update(desired_capacity: @group.desired_capacity + @opts[:num_simultaneous_instances])
 
       puts "The list of instances in Auto Scaling Group #{@group.name} that will be terminated is:\n#{@group.auto_scaling_instances.map{ |i| i.ec2_instance.id }.to_ary}"
-      @group.auto_scaling_instances.each_slice(@opts[:num_simultaneous_instances]) do |instances|
+      @group.auto_scaling_instances.to_a.each_slice(@opts[:num_simultaneous_instances]) do |instances|
         time_taken = 0
 
         until all_instances_inservice_for_time_period?(@group.load_balancers, INSERVICE_POLLING_TIME)
diff --git a/spec/support/fake_auto_scaling.rb b/spec/support/fake_auto_scaling.rb
index 6fe7aa1..30dcae6 100644
--- a/spec/support/fake_auto_scaling.rb
+++ b/spec/support/fake_auto_scaling.rb
@@ -48,7 +48,7 @@ module AWS
       end
 
       def auto_scaling_instances
-        @auto_scaling_instances ||= [AWS::FakeAutoScaling::Instance.new(self), AWS::FakeAutoScaling::Instance.new(self)]
+        @auto_scaling_instances ||= AWS::FakeCore::Data::List.new [AWS::FakeAutoScaling::Instance.new(self), AWS::FakeAutoScaling::Instance.new(self)]
       end
 
       def load_balancers
diff --git a/spec/support/fake_core_data_list.rb b/spec/support/fake_core_data_list.rb
new file mode 100644
index 0000000..e23c996
--- /dev/null
+++ b/spec/support/fake_core_data_list.rb
@@ -0,0 +1,71 @@
+module AWS
+  module FakeCore
+    class Data
+      module MethodMissingProxy
+
+        protected
+
+        def method_missing *args, &block
+          if block_given?
+            return_value = @data.send(*args) do |*values|
+              yield(*values.flatten.map{|v| Data.cast(v) })
+            end
+            Data.cast(return_value)
+          else
+            Data.cast(@data.send(*args))
+          end
+        end
+
+      end
+
+      include MethodMissingProxy
+
+      def method_missing method_name, *args, &block
+        if
+          args.empty? and !block_given? and
+          key = _remove_question_mark(method_name) and
+          @data.has_key?(key)
+        then
+          Data.cast(@data[key])
+        else
+          super
+        end
+      end
+
+      class << self
+
+        # Given a hash, this method returns a {Data} object.  Given
+        # an Array, this method returns a {Data::List} object.  Everything
+        # else is returned as is.
+        #
+        # @param [Object] value The value to conditionally wrap.
+        #
+        # @return [Data,Data::List,Object] Wraps hashes and lists with
+        #   Data and List objects, all other objects are returned as
+        #   is.
+        #
+        def cast value
+          case value
+          when Hash then Data.new(value)
+          when Array then Data::List.new(value)
+          else value
+          end
+        end
+
+      end
+
+      class List
+        include MethodMissingProxy
+
+        def initialize(array)
+          @data = array
+        end
+
+        def to_ary
+          @data
+        end
+        alias_method :to_a, :to_ary
+      end
+    end
+  end
+end