Merge remote-tracking branch 'origin/tp31'
diff --git a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/ExpandableStepIterator.java b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/ExpandableStepIterator.java
index dc61ad2..30558e8 100644
--- a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/ExpandableStepIterator.java
+++ b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/ExpandableStepIterator.java
@@ -28,7 +28,7 @@
 /**
  * @author Marko A. Rodriguez (http://markorodriguez.com)
  */
-public class ExpandableStepIterator<S> implements Iterator<Traverser.Admin<S>>, Serializable {
+public final class ExpandableStepIterator<S> implements Iterator<Traverser.Admin<S>>, Serializable {
 
     private final TraverserSet<S> traverserSet = new TraverserSet<>();
     private final Step<S, ?> hostStep;