diff --git a/src/jrummikub/model/StoneSet.java b/src/jrummikub/model/StoneSet.java
index 83ce767..b798ad0 100644
--- a/src/jrummikub/model/StoneSet.java
+++ b/src/jrummikub/model/StoneSet.java
@@ -7,8 +7,6 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 
-import sun.reflect.generics.reflectiveObjects.NotImplementedException;
-
 import jrummikub.util.Pair;
 import static jrummikub.model.StoneSet.Type.*;
 
@@ -219,7 +217,7 @@ public class StoneSet implements Iterable<Stone>, Sizeable {
 			public void remove() {
 				// removing stones is impossible
 
-				throw new NotImplementedException();
+				throw new UnsupportedOperationException();
 			}
 		};
 	}