diff --git a/test/ruby/test_transcode.rb b/test/ruby/test_transcode.rb
index e88979a681..db91010c94 100644
--- a/test/ruby/test_transcode.rb
+++ b/test/ruby/test_transcode.rb
@@ -2068,6 +2068,7 @@ class TestTranscode < Test::Unit::TestCase
   %w[UTF-32 UTF-16].each do |enc|
     define_method("test_pseudo_encoding_inspect(#{enc})") do
       assert_normal_exit("'aaa'.encode('#{enc}').inspect", bug8940)
+      assert_equal(4, 'aaa'.encode(enc).length, "should count in #{enc} with BOM")
     end
   end
 end