diff --git a/file.c b/file.c
index 8bca84283d..c576c85c0a 100644
--- a/file.c
+++ b/file.c
@@ -6134,7 +6134,7 @@ Init_File(void)
     rb_define_const(rb_mFConst, "LOCK_NB", INT2FIX(LOCK_NB));
 
     /* Name of the null device */
-    rb_define_const(rb_mFConst, "NULL", rb_obj_freeze(rb_usascii_str_new2(null_device)));
+    rb_define_const(rb_mFConst, "NULL", rb_fstring_cstr(null_device));
 
     rb_define_method(rb_cFile, "path",  rb_file_path, 0);
     rb_define_method(rb_cFile, "to_path",  rb_file_path, 0);