diff --git a/src/error.c b/src/error.c
index 40abc2a84d..8773f13477 100644
--- a/src/error.c
+++ b/src/error.c
@@ -137,10 +137,9 @@ exc_to_s(mrb_state *mrb, mrb_value exc)
 mrb_value
 mrb_exc_inspect(mrb_state *mrb, mrb_value exc)
 {
-  mrb_value mesg = mrb_exc_mesg_get(mrb, mrb_exc_ptr(exc));
   mrb_value cname = mrb_mod_to_s(mrb, mrb_obj_value(mrb_obj_class(mrb, exc)));
-  mesg = mrb_obj_as_string(mrb, mesg);
-  return RSTRING_LEN(mesg) == 0 ? cname : mrb_format(mrb, "%v (%v)", mesg, cname);
+  mrb_value mesg = mrb_exc_mesg_get(mrb, mrb_exc_ptr(exc)); /* string or nil */
+  return (mrb_nil_p(mesg)||RSTRING_LEN(mesg)==0) ? cname : mrb_format(mrb, "%v (%v)", mesg, cname);
 }
 
 void mrb_keep_backtrace(mrb_state *mrb, mrb_value exc);