Index: trunk/src/org/openstreetmap/josm/actions/CombineWayAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/CombineWayAction.java	(revision 16731)
+++ trunk/src/org/openstreetmap/josm/actions/CombineWayAction.java	(revision 16732)
@@ -131,5 +131,5 @@
 
         // try to build a new way which includes all the combined ways
-        List<Node> path = tryJoin(ways);
+        List<Node> path = new LinkedList<>(tryJoin(ways));
         if (path.isEmpty()) {
             warnCombiningImpossible();