diff --git a/mrbgems/mruby-string-utf8/test/string.rb b/mrbgems/mruby-string-utf8/test/string.rb
index 1bfa8512c..ad864410a 100644
--- a/mrbgems/mruby-string-utf8/test/string.rb
+++ b/mrbgems/mruby-string-utf8/test/string.rb
@@ -66,3 +66,7 @@ assert('String#rindex') do
   assert_equal 12, str.rindex('ち')
   assert_equal 3, str.rindex('ち', 10)
 end
+
+assert('String#chr') do
+  assert_equal "こ", "こんにちは世界!".chr
+end