Fix that `Module#to_s` may return frozen string; ref 08eafe2

1 files changed, 2 insertions, 1 deletions

diff --git a/src/class.c b/src/class.c
index b1c7513de..b8d3d31d8 100644
--- a/src/class.c
+++ b/src/class.c
@@ -1885,7 +1885,8 @@ mrb_mod_to_s(mrb_state *mrb, mrb_value klass)
     return mrb_str_cat_lit(mrb, str, ">");
   }
   else {
-    return class_name_str(mrb, mrb_class_ptr(klass));
+    mrb_value str = class_name_str(mrb, mrb_class_ptr(klass));
+    return mrb_frozen_p(mrb_basic_ptr(str)) ? mrb_str_dup(mrb, str) : str;
   }
 }