diff --git a/com.avaloq.tools.ddk.typesystem/src/com/avaloq/tools/ddk/typesystem/BuiltInTypeModelAccess.java b/com.avaloq.tools.ddk.typesystem/src/com/avaloq/tools/ddk/typesystem/BuiltInTypeModelAccess.java
index 07f80c39d..f30ca0cc0 100644
--- a/com.avaloq.tools.ddk.typesystem/src/com/avaloq/tools/ddk/typesystem/BuiltInTypeModelAccess.java
+++ b/com.avaloq.tools.ddk.typesystem/src/com/avaloq/tools/ddk/typesystem/BuiltInTypeModelAccess.java
@@ -14,7 +14,7 @@
 import java.util.Map;
 
 import org.apache.logging.log4j.Logger;
-import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.LogManager;
 import org.eclipse.emf.common.util.URI;
 import org.eclipse.emf.ecore.resource.Resource;
 import org.eclipse.emf.ecore.resource.ResourceSet;
@@ -62,7 +62,7 @@ public final class BuiltInTypeModelAccess {
   /**
    * The singleton instance.
    */
-  private static class InstanceHolder {
+  private static final class InstanceHolder {
     // Initialize-on-demand holder pattern.
     @SuppressWarnings("PMD.AccessorClassGeneration")
     // This is a common idiom, and PMD even says to use it, see http://pmd.sourceforge.net/pmd-5.1.0/rules/java/design.html, Rule NonThreadSafeSingleton