diff --git a/lib/vm/parfait/class.rb b/lib/vm/parfait/class.rb
index fd06bd97..d6dfcd34 100644
--- a/lib/vm/parfait/class.rb
+++ b/lib/vm/parfait/class.rb
@@ -42,7 +42,12 @@ module Parfait
     def get_method(name)
       @methods[name]
     end
-    
+
+    # adding an instance changes the instance_type to include that variable
+    def add_instance_variable( name , type)
+      @instance_type = @instance_type.add_instance_variable( name , type )
+    end
+
     # setting the type generates all methods for this type
     # (or will do, once we store the methods code to do that)
     def set_instance_type( type )
diff --git a/test/vm/parfait/test_class.rb b/test/vm/parfait/test_class.rb
index 4e27ead5..80b2a654 100644
--- a/test/vm/parfait/test_class.rb
+++ b/test/vm/parfait/test_class.rb
@@ -34,4 +34,15 @@ class TestClass < MiniTest::Test
   def test_add_method
     assert_raises{ @try.add_instance_method(nil)}
   end
+  def test_add_instance_variable_changes_type
+    before = @space.get_class.instance_type
+    @space.get_class.add_instance_variable(:counter , :Integer)
+    assert before != @space.get_class.instance_type
+  end
+  def test_add_instance_variable_changes_type_hash
+    before = @space.get_class.instance_type.hash
+    @space.get_class.add_instance_variable(:counter , :Integer)
+    assert before != @space.get_class.instance_type.hash
+  end
+
 end