diff --git a/src/error.c b/src/error.c
index cce382537..b76f17369 100644
--- a/src/error.c
+++ b/src/error.c
@@ -592,18 +592,20 @@ mrb_make_exception(mrb_state *mrb, mrb_value exc, mrb_value mesg)
 MRB_API mrb_noreturn void
 mrb_sys_fail(mrb_state *mrb, const char *mesg)
 {
+  mrb_int no = (mrb_int)errno;
+  mrb_value mesg_str = mesg ? mrb_str_new_cstr(mrb, mesg) : mrb_nil_value();
+
   if (mrb_class_defined_id(mrb, MRB_SYM(SystemCallError))) {
     struct RClass *sce = mrb_class_get_id(mrb, MRB_SYM(SystemCallError));
-    mrb_int no = (mrb_int)errno;
     if (mesg != NULL) {
-      mrb_funcall_id(mrb, mrb_obj_value(sce), MRB_SYM(_sys_fail), 2, mrb_fixnum_value(no), mrb_str_new_cstr(mrb, mesg));
+      mrb_funcall_id(mrb, mrb_obj_value(sce), MRB_SYM(_sys_fail), 2, mrb_fixnum_value(no), mesg_str);
     }
     else {
       mrb_funcall_id(mrb, mrb_obj_value(sce), MRB_SYM(_sys_fail), 1, mrb_fixnum_value(no));
     }
   }
 
-  mrb_raise(mrb, E_RUNTIME_ERROR, mesg);
+  mrb_exc_raise(mrb, mrb_exc_new_str(mrb, E_RUNTIME_ERROR, mesg ? mesg_str : mrb_str_new_lit(mrb, "")));
 }
 
 /*