diff --git a/lib/propane/parser/item_set.rb b/lib/propane/parser/item_set.rb
index df85c41..12139d6 100644
--- a/lib/propane/parser/item_set.rb
+++ b/lib/propane/parser/item_set.rb
@@ -112,13 +112,11 @@ class Propane
       def close!
         eval_items = @items
         while eval_items.size > 0
-          this_eval_items = eval_items
-          eval_items = Set.new
-          this_eval_items.each do |item|
-            item.closed_items.each do |new_item|
-              unless @items.include?(new_item)
-                eval_items << new_item
-              end
+          item = eval_items.first
+          eval_items.delete(item)
+          item.closed_items.each do |new_item|
+            unless @items.include?(new_item)
+              eval_items << new_item
             end
           end
           @items += eval_items