diff --git a/dev/checkstyle/checkstyle.xml b/dev/checkstyle/checkstyle.xml
index 6db0a94..117cacd 100644
--- a/dev/checkstyle/checkstyle.xml
+++ b/dev/checkstyle/checkstyle.xml
@@ -33,7 +33,6 @@
     <!-- File must start with the C Thing copyright header -->
     <module name="RegexpHeader">
         <property name="headerFile" value="${config_loc}/header.txt"/>
-        <property name="multiLines" value="3"/>
     </module>
 
     <!-- Flag IDE generated comments -->
diff --git a/dev/checkstyle/header.txt b/dev/checkstyle/header.txt
index c2f20d0..e8554b3 100644
--- a/dev/checkstyle/header.txt
+++ b/dev/checkstyle/header.txt
@@ -1,16 +1,4 @@
 ^/\*$
 ^ \* Copyright [\d]{4}((,[\s]*[\d]{4})*|(-[\d]{4})?) C Thing Software$
-^ \* .*
-^ \*$
-^ \* Licensed under the Apache License, Version 2\.0 \(the "License"\);$
-^ \* you may not use this file except in compliance with the License\.$
-^ \* You may obtain a copy of the License at$
-^ \*$
-^ \*     http://www\.apache\.org/licenses/LICENSE-2\.0$
-^ \*$
-^ \* Unless required by applicable law or agreed to in writing, software$
-^ \* distributed under the License is distributed on an "AS IS" BASIS,$
-^ \* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied\.$
-^ \* See the License for the specific language governing permissions and$
-^ \* limitations under the License\.$
+^ \* SPDX-License-Identifier: Apache-2.0$
 ^ \*/$
diff --git a/src/main/java/org/cthing/xmlwriter/XmlAttributes.java b/src/main/java/org/cthing/xmlwriter/XmlAttributes.java
index 86e09a2..05ff25c 100644
--- a/src/main/java/org/cthing/xmlwriter/XmlAttributes.java
+++ b/src/main/java/org/cthing/xmlwriter/XmlAttributes.java
@@ -1,17 +1,6 @@
 /*
  * Copyright 2022 C Thing Software
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 package org.cthing.xmlwriter;
 
diff --git a/src/main/java/org/cthing/xmlwriter/XmlWriter.java b/src/main/java/org/cthing/xmlwriter/XmlWriter.java
index 6f66033..1083d83 100755
--- a/src/main/java/org/cthing/xmlwriter/XmlWriter.java
+++ b/src/main/java/org/cthing/xmlwriter/XmlWriter.java
@@ -1,17 +1,6 @@
 /*
  * Copyright 2022 C Thing Software
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 package org.cthing.xmlwriter;
 
@@ -615,7 +604,6 @@ public void flush() throws SAXException {
      *         output is used.
      * @return The newly set writer.
      */
-    @SuppressWarnings({ "resource", "IOResourceOpenedButNotSafelyClosed" })
     public final Writer setOutput(@Nullable @WillNotClose final Writer writer) {
         this.out = (writer == null) ? new OutputStreamWriter(System.out, StandardCharsets.UTF_8) : writer;
         return this.out;
@@ -2501,7 +2489,6 @@ private void writeName(final String uri, final String localName, final String qN
      * @return Number of namespace declaration attributes written
      * @throws SAXException If there is a problem writing the namespaces.
      */
-    @SuppressWarnings("unchecked")
     private int writeNSDecls() throws SAXException {
         // Since the iteration order for namespaces is not stable, sort them.
         final List<String> prefixes = Collections.list(this.nsSupport.getDeclaredPrefixes());
diff --git a/src/main/java/org/cthing/xmlwriter/package-info.java b/src/main/java/org/cthing/xmlwriter/package-info.java
index 18791ce..dbbaf3e 100644
--- a/src/main/java/org/cthing/xmlwriter/package-info.java
+++ b/src/main/java/org/cthing/xmlwriter/package-info.java
@@ -1,17 +1,6 @@
 /*
  * Copyright 2022 C Thing Software
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 
 /**
diff --git a/src/test/java/org/cthing/xmlwriter/XmlAttributesTest.java b/src/test/java/org/cthing/xmlwriter/XmlAttributesTest.java
index ef0a33e..33900ce 100644
--- a/src/test/java/org/cthing/xmlwriter/XmlAttributesTest.java
+++ b/src/test/java/org/cthing/xmlwriter/XmlAttributesTest.java
@@ -1,17 +1,6 @@
 /*
  * Copyright 2022 C Thing Software
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 package org.cthing.xmlwriter;
 
diff --git a/src/test/java/org/cthing/xmlwriter/XmlWriterTest.java b/src/test/java/org/cthing/xmlwriter/XmlWriterTest.java
index 706244c..3e00243 100755
--- a/src/test/java/org/cthing/xmlwriter/XmlWriterTest.java
+++ b/src/test/java/org/cthing/xmlwriter/XmlWriterTest.java
@@ -1,17 +1,6 @@
 /*
  * Copyright 2022 C Thing Software
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * SPDX-License-Identifier: Apache-2.0
  */
 package org.cthing.xmlwriter;