diff --git a/core/api/src/main/java/org/onlab/onos/store/Timestamp.java b/core/api/src/main/java/org/onlab/onos/store/Timestamp.java
index b9d3648..b3caf85 100644
--- a/core/api/src/main/java/org/onlab/onos/store/Timestamp.java
+++ b/core/api/src/main/java/org/onlab/onos/store/Timestamp.java
@@ -2,7 +2,15 @@
 
 /**
  * Opaque version structure.
+ * <p>
+ * Classes implementing this interface must also implement
+ * {@link #hashCode()} and {@link #equals(Object)}.
  */
 public interface Timestamp extends Comparable<Timestamp> {
 
+    @Override
+    public abstract int hashCode();
+
+    @Override
+    public abstract boolean equals(Object obj);
 }