Attached test case demonstrates. Here it is for easy browsing: public static class Aquarium extends StandardObject { private String name; private LinkedList fish = new LinkedList(); public Aquarium(String name) { this.name = name; } public void addFish(String fish) { this.fish.add(fish); } } public void testMatchingXmlElementAndJavaFieldName() { Aquarium aquarium = new Aquarium("hatchery"); aquarium.addFish("salmon"); aquarium.addFish("halibut"); aquarium.addFish("snapper"); String expected = "" + "<aquarium>\n" + " <name>hatchery</name>\n" + " <fish>salmon</fish>\n" + " <fish>halibut</fish>\n" + " <fish>snapper</fish>\n" + "</aquarium>"; xstream.alias("aquarium", Aquarium.class); xstream.addImplicitCollection(Aquarium.class, "fish", "fish", String.class); assertBothWays(aquarium, expected); } Results in this error: com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$DuplicateFieldException: fish ---- Debugging information ---- required-type : com.thoughtworks.acceptance.ImplicitCollectionTest$Aquarium class : com.thoughtworks.acceptance.ImplicitCollectionTest$Aquarium line number : 4 path : /aquarium/fish[2] ------------------------------- at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$SeenFields.add(AbstractReflectionConverter.java:234) at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doUnmarshal(AbstractReflectionConverter.java:167) at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshal(AbstractReflectionConverter.java:117) at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:56) at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:45) at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:46) at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:117) at com.thoughtworks.xstream.core.ReferenceByXPathMarshallingStrategy.unmarshal(ReferenceByXPathMarshallingStrategy.java:29) at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:789) at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:777) at com.thoughtworks.xstream.XStream.fromXML(XStream.java:731) at com.thoughtworks.xstream.XStream.fromXML(XStream.java:724)