diff --git a/test/t/string.rb b/test/t/string.rb
index f38790c17..ee969a696 100644
--- a/test/t/string.rb
+++ b/test/t/string.rb
@@ -319,3 +319,11 @@ assert('String#upcase!', '15.2.10.5.43') do
 
   a == 'ABC'
 end
+
+# Not ISO specified
+
+assert('String interpolation (mrb_str_concat for shared strings)') do
+  a = "A" * 32
+  "#{a}:" == "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA:"
+end
+