diff --git a/drivers/default/src/main/java/org/onosproject/driver/extensions/NiciraMatchCtState.java b/drivers/default/src/main/java/org/onosproject/driver/extensions/NiciraMatchCtState.java
index eb4c6da..f2fb423 100644
--- a/drivers/default/src/main/java/org/onosproject/driver/extensions/NiciraMatchCtState.java
+++ b/drivers/default/src/main/java/org/onosproject/driver/extensions/NiciraMatchCtState.java
@@ -16,6 +16,7 @@
 
 package org.onosproject.driver.extensions;
 
+import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
 
@@ -34,7 +35,9 @@
     private long ctState;
     private long ctStateMask;
 
-    private final KryoNamespace appKryo = new KryoNamespace.Builder().build();
+    private final KryoNamespace appKryo = new KryoNamespace.Builder()
+                                                .register(HashMap.class)
+                                                .build();
 
     /**
      * Creates a new conntrack state selector.