diff --git a/test/mrb_set.rb b/test/mrb_set.rb
index 60484385c..0751d08d7 100644
--- a/test/mrb_set.rb
+++ b/test/mrb_set.rb
@@ -209,7 +209,7 @@ assert("Set#flatten!") do
     set1.flatten!
   }
 
-  # test5; miscellaneous
+  # test4; miscellaneous
   assert_nil(Set.new(0..31).flatten!)
 
   x = Set[Set[],Set[1,2]].flatten!