diff --git a/utils/misc/src/main/java/org/onlab/util/DefaultHashMap.java b/utils/misc/src/main/java/org/onlab/util/DefaultHashMap.java
index f9d878a..d6ddbd5 100644
--- a/utils/misc/src/main/java/org/onlab/util/DefaultHashMap.java
+++ b/utils/misc/src/main/java/org/onlab/util/DefaultHashMap.java
@@ -21,10 +21,10 @@
 /**
  * HashMap that returns a default value for unmapped keys.
  */
-public class DefaultHashMap<K, V> extends HashMap<K, V> {
+public final class DefaultHashMap<K, V> extends HashMap<K, V> {
 
     /** Default value to return when no key binding exists. */
-    protected V defaultValue;
+    protected final V defaultValue;
 
     /**
      * Constructs an empty map with the given default value.