From d7a6ff8224519005d2deeb3f4e98689a8a0835ad Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Sat, 3 Jan 2026 15:03:57 +0900
Subject: [PATCH] [Bug #21819] Data objects without members should also be
 frozen

---
 struct.c               | 1 +
 test/ruby/test_data.rb | 1 +
 2 files changed, 2 insertions(+)

diff --git a/struct.c b/struct.c
index 667d35424f..31df3798cb 100644
--- a/struct.c
+++ b/struct.c
@@ -1809,6 +1809,7 @@ rb_data_initialize_m(int argc, const VALUE *argv, VALUE self)
         if (num_members > 0) {
             rb_exc_raise(rb_keyword_error_new("missing", members));
         }
+        OBJ_FREEZE(self);
         return Qnil;
     }
     if (argc > 1 || !RB_TYPE_P(argv[0], T_HASH)) {
diff --git a/test/ruby/test_data.rb b/test/ruby/test_data.rb
index dd698fdcc4..5ac4c6b84b 100644
--- a/test/ruby/test_data.rb
+++ b/test/ruby/test_data.rb
@@ -262,6 +262,7 @@ class TestData < Test::Unit::TestCase
     assert_equal('#<data >', test.inspect)
     assert_equal([], test.members)
     assert_equal({}, test.to_h)
+    assert_predicate(test, :frozen?)
   end
 
   def test_dup