diff --git a/test/test_sorted_set.rb b/test/test_sorted_set.rb
index f7ad7af..09a1e7a 100644
--- a/test/test_sorted_set.rb
+++ b/test/test_sorted_set.rb
@@ -42,4 +42,4 @@ def test_ok_require
       var = SortedSet.new.to_s
     RUBY
   end
-end
+end if defined?(SortedSet)