diff --git a/dev/checkstyle/header.txt b/dev/checkstyle/header.txt
index 3830649..e8554b3 100644
--- a/dev/checkstyle/header.txt
+++ b/dev/checkstyle/header.txt
@@ -1,4 +1,4 @@
 ^/\*$
 ^ \* Copyright [\d]{4}((,[\s]*[\d]{4})*|(-[\d]{4})?) C Thing Software$
-^ \* PDX-License-Identifier: Apache-2.0$
+^ \* SPDX-License-Identifier: Apache-2.0$
 ^ \*/$
diff --git a/src/main/java/org/cthing/projectversion/BuildType.java b/src/main/java/org/cthing/projectversion/BuildType.java
index 44de99d..9382dc9 100644
--- a/src/main/java/org/cthing/projectversion/BuildType.java
+++ b/src/main/java/org/cthing/projectversion/BuildType.java
@@ -1,6 +1,6 @@
 /*
  * Copyright 2024 C Thing Software
- * PDX-License-Identifier: Apache-2.0
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 package org.cthing.projectversion;
diff --git a/src/main/java/org/cthing/projectversion/ProjectVersion.java b/src/main/java/org/cthing/projectversion/ProjectVersion.java
index 629954a..bdcb0b3 100644
--- a/src/main/java/org/cthing/projectversion/ProjectVersion.java
+++ b/src/main/java/org/cthing/projectversion/ProjectVersion.java
@@ -1,6 +1,6 @@
 /*
  * Copyright 2024 C Thing Software
- * PDX-License-Identifier: Apache-2.0
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 package org.cthing.projectversion;
diff --git a/src/main/java/org/cthing/projectversion/package-info.java b/src/main/java/org/cthing/projectversion/package-info.java
index 979ef4a..b507057 100644
--- a/src/main/java/org/cthing/projectversion/package-info.java
+++ b/src/main/java/org/cthing/projectversion/package-info.java
@@ -1,6 +1,6 @@
 /*
  * Copyright 2024 C Thing Software
- * PDX-License-Identifier: Apache-2.0
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 /**
diff --git a/src/test/java/org/cthing/projectversion/ProjectVersionTest.java b/src/test/java/org/cthing/projectversion/ProjectVersionTest.java
index e553fc7..dd3315d 100644
--- a/src/test/java/org/cthing/projectversion/ProjectVersionTest.java
+++ b/src/test/java/org/cthing/projectversion/ProjectVersionTest.java
@@ -1,6 +1,6 @@
 /*
  * Copyright 2024 C Thing Software
- * PDX-License-Identifier: Apache-2.0
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 package org.cthing.projectversion;