diff --git a/core/api/src/main/java/org/onlab/onos/net/flow/TrafficSelector.java b/core/api/src/main/java/org/onlab/onos/net/flow/TrafficSelector.java
index 249d1f9..c704c8f 100644
--- a/core/api/src/main/java/org/onlab/onos/net/flow/TrafficSelector.java
+++ b/core/api/src/main/java/org/onlab/onos/net/flow/TrafficSelector.java
@@ -1,6 +1,6 @@
 package org.onlab.onos.net.flow;
 
-import java.util.List;
+import java.util.Set;
 
 import org.onlab.onos.net.PortNumber;
 import org.onlab.onos.net.flow.criteria.Criterion;
@@ -18,7 +18,7 @@
      *
      * @return list of criteria
      */
-    List<Criterion> criteria();
+    Set<Criterion> criteria();
 
     /**
      * Builder of traffic selector entities.