diff --git a/.github/workflows/linux-clang.yml b/.github/workflows/linux-clang.yml
index c1cbe5ea..53a92e51 100644
--- a/.github/workflows/linux-clang.yml
+++ b/.github/workflows/linux-clang.yml
@@ -1,6 +1,6 @@
 # GitHub Actions Workflow
 # Build with Clang on Linux
-# Copyright 2019-2026 kaoru  https://www.tetengo.org/
+# Copyright (C) 2019-2026 kaoru  https://www.tetengo.org/
 
 name: Linux - Clang
 
diff --git a/.github/workflows/linux-gcc.yml b/.github/workflows/linux-gcc.yml
index e62d1d9d..1268cb05 100644
--- a/.github/workflows/linux-gcc.yml
+++ b/.github/workflows/linux-gcc.yml
@@ -1,6 +1,6 @@
 # GitHub Actions Workflow
 # Build with GCC on Linux
-# Copyright 2019-2026 kaoru  https://www.tetengo.org/
+# Copyright (C) 2019-2026 kaoru  https://www.tetengo.org/
 
 name: Linux - GCC
 
diff --git a/.github/workflows/windows-visualcpp.yml b/.github/workflows/windows-visualcpp.yml
index e505a88e..6809cd9a 100644
--- a/.github/workflows/windows-visualcpp.yml
+++ b/.github/workflows/windows-visualcpp.yml
@@ -1,6 +1,6 @@
 # GitHub Actions Workflow
 # Build with Visual C++ on Windows
-# Copyright 2019-2026 kaoru  https://www.tetengo.org/
+# Copyright (C) 2019-2026 kaoru  https://www.tetengo.org/
 
 name: Windows - Visual C++