diff --git a/README.md b/README.md
old mode 100755
new mode 100644
index 74d6271..b273a56
--- a/README.md
+++ b/README.md
@@ -123,5 +123,10 @@ CI（GitHub Actions）は両方のテストと `npm run build` を回します
 
 ## ライセンス
 
-MIT。コマンド列エンコーダは [dz-print](https://github.com/sb-child/dz-print)（MIT）の
-実装を参照しています。
+本プロジェクトは **MIT** です。ただしコマンド列エンコーダ
+（`src/dzpost/protocol.py` / `web/src/protocol.ts`）は
+[dz-print](https://github.com/sb-child/dz-print)（**MPL-2.0**）の派生物なので、
+この 2 ファイルだけ **MPL-2.0** が適用されます（ファイル単位のコピーレフト）。
+
+- `LICENSE` — MIT（上記 2 ファイル以外）
+- MPL-2.0 の全文 — <https://mozilla.org/MPL/2.0/>
diff --git a/README.zh-CN.md b/README.zh-CN.md
old mode 100755
new mode 100644
index 73ddbbd..cb37ddf
--- a/README.zh-CN.md
+++ b/README.zh-CN.md
@@ -114,4 +114,9 @@ CI（GitHub Actions）会跑两边的测试和构建。
 
 ## 许可
 
-MIT。命令流编码参考了 [dz-print](https://github.com/sb-child/dz-print)（MIT）。
+本项目整体为 **MIT**。但命令流编码器（`src/dzpost/protocol.py` / `web/src/protocol.ts`）
+是 [dz-print](https://github.com/sb-child/dz-print)（**MPL-2.0**）的衍生作品，
+这两个文件单独适用 **MPL-2.0**（文件级 copyleft）。
+
+- `LICENSE` — MIT（上述两个文件之外）
+- MPL-2.0 全文 — <https://mozilla.org/MPL/2.0/>
diff --git a/docs/PROTOCOL.md b/docs/PROTOCOL.md
old mode 100755
new mode 100644
index 5b27f5a..40d96cc
--- a/docs/PROTOCOL.md
+++ b/docs/PROTOCOL.md
@@ -1,7 +1,7 @@
 # 协议速查
 
 来源：DeTong DP305P（`3533:5C32`，序列号 `DP305P-Y60870279`）真机逆向，
-以及 `dz-print`（MIT）的参考实现。完整逆向记录见原工作区
+以及 `dz-print`（**MPL-2.0**）的参考实现。完整逆向记录见原工作区
 `DeTong/REPORT.md`、`DeTong/analysis/ble.md`、`DeTong/dz-print/protocol.md`。
 
 ## 命令帧（USB / BLE 相同）
diff --git a/pyproject.toml b/pyproject.toml
index 0c7faf6..65d10e8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,7 +8,7 @@ version = "0.1.0"
 description = "Print Japan Post ClickPost labels on a DeTong DP-series label printer"
 readme = "README.md"
 requires-python = ">=3.10"
-license = { text = "MIT" }
+license = { text = "MIT AND MPL-2.0" }
 authors = [{ name = "clickpost-printer contributors" }]
 keywords = ["clickpost", "japan-post", "label-printer", "thermal-printer", "ble", "web-bluetooth"]
 classifiers = [
@@ -16,6 +16,7 @@ classifiers = [
     "Environment :: Console",
     "Intended Audience :: End Users/Desktop",
     "License :: OSI Approved :: MIT License",
+    "License :: OSI Approved :: Mozilla Public License 2.0 (MPL 2.0)",
     "Operating System :: MacOS",
     "Operating System :: POSIX :: Linux",
     "Programming Language :: Python :: 3",
diff --git a/src/dzpost/protocol.py b/src/dzpost/protocol.py
index f709f3e..b4dd0e6 100644
--- a/src/dzpost/protocol.py
+++ b/src/dzpost/protocol.py
@@ -1,8 +1,16 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# Derived from dz-print <https://github.com/sb-child/dz-print> (MPL-2.0),
+# notably src/image_proc/cmd_parser.rs and src/command/.  Only this file is
+# under MPL-2.0; the rest of this project stays MIT.
+
 """DeTong DP-series label printer command stream.
 
 Everything here was reverse-engineered against a DeTong DP305P
 (``3533:5C32``, 300 dpi, 960-dot head) and is byte-compatible with the
-reference implementation in ``dz-print`` (MIT).
+reference implementation in ``dz-print`` (MPL-2.0).
 
 Two layers of framing exist on the wire:
 
diff --git a/web/src/protocol.ts b/web/src/protocol.ts
index cc9ee7e..4199b5c 100644
--- a/web/src/protocol.ts
+++ b/web/src/protocol.ts
@@ -1,3 +1,11 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+//
+// Derived from dz-print <https://github.com/sb-child/dz-print> (MPL-2.0)
+// via src/dzpost/protocol.py.  Only this file is under MPL-2.0; the rest of
+// this project stays MIT.
+
 /**
  * DeTong DP-series label printer command stream.
  *