diff --git a/mrbgems/mruby-numeric-ext/test/numeric.rb b/mrbgems/mruby-numeric-ext/test/numeric.rb
index cafa0f1aa..0132e5559 100644
--- a/mrbgems/mruby-numeric-ext/test/numeric.rb
+++ b/mrbgems/mruby-numeric-ext/test/numeric.rb
@@ -4,4 +4,7 @@
 assert('Integer#chr') do
   assert_equal(65.chr, "A")
   assert_equal(0x42.chr, "B")
+
+  # encoding multibyte (not support yet)
+  assert_raise(RangeError) { 12345.chr }
 end