diff --git a/pmd-core/src/main/java/net/sourceforge/pmd/util/treeexport/TreeExportCli.java b/pmd-core/src/main/java/net/sourceforge/pmd/util/treeexport/TreeExportCli.java
index 2916bde9e0..cd7c7c7e99 100644
--- a/pmd-core/src/main/java/net/sourceforge/pmd/util/treeexport/TreeExportCli.java
+++ b/pmd-core/src/main/java/net/sourceforge/pmd/util/treeexport/TreeExportCli.java
@@ -227,7 +227,7 @@ public class TreeExportCli {
         return new AbortedError();
     }
 
-    private static class AbortedError extends Error {
+    private static final class AbortedError extends Error {
 
     }
 }