diff --git a/spec/runtime/interval_skip_list/insert_spec.rb b/spec/runtime/interval_skip_list/insert_spec.rb
index 9e236c2..c6eddd4 100644
--- a/spec/runtime/interval_skip_list/insert_spec.rb
+++ b/spec/runtime/interval_skip_list/insert_spec.rb
@@ -1,6 +1,6 @@
 require 'runtime/interval_skip_list/spec_helper'
 
-describe IntervalSkipList, " when #next_node_height returns 1, 3, 2, 3, 1 in order" do
+describe IntervalSkipList, " when #next_node_height returns 1, 3, 2, 3, 1 in order", :deterministic2 => true do
   include IntervalSkipListSpecHelper
   attr_reader :list, :node