Map works but Map fails (CXF 2.6.2)

I have a CXF 2.6.2 web service that works fine returning a List of custom
result objects, each of which contains (among other things) a member of
type Map<String, String>. Like this:

public class Result {

...

private Map<String, String> definition;

...

public Map<String, String> getDefinition() {
return definition;

public void setDefinition(Map<String, String> definition) {
this.definition = definition;

...

But, if I change the type of "definition" above to Map<String, Object> (and
the accessors and other dependent code, of course) it fails with the
exception below.

Any ideas?

javax.xml.bind.JAXBException: class java.util.HashMap nor any of its super
class is known to this context.]
at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:326)
at
com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:251)
at
javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:75)
at
org.apache.cxf.jaxb.JAXBEncoderDecoder.writeObject(JAXBEncoderDecoder.java:554)
at
org.apache.cxf.jaxb.JAXBEncoderDecoder.marshall(JAXBEncoderDecoder.java:236)
at org.apache.cxf.jaxb.io.DataWriterImpl.write(DataWriterImpl.java:168)
at
org.apache.cxf.interceptor.AbstractOutDatabindingInterceptor.writeParts(AbstractOutDatabindingInterceptor.java:110)
at
org.apache.cxf.interceptor.BareOutInterceptor.handleMessage(BareOutInterceptor.java:68)
at
org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:262)
at
org.apache.cxf.interceptor.OutgoingChainInterceptor.handleMessage(OutgoingChainInterceptor.java:77)
at
org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:262)
at
org.apache.cxf.transport.ChainInitiationObserver.onMessage(ChainInitiationObserver.java:121)
at
org.apache.cxf.transport.http.AbstractHTTPDestination.invoke(AbstractHTTPDestination.java:211)
at
org.apache.cxf.transport.servlet.ServletController.invokeDestination(ServletController.java:213)
at
org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:193)
at
org.apache.cxf.transport.servlet.CXFNonSpringServlet.invoke(CXFNonSpringServlet.java:130)
at
org.apache.cxf.transport.servlet.AbstractHTTPServlet.handleRequest(AbstractHTTPServlet.java:221)
at
org.apache.cxf.transport.servlet.AbstractHTTPServlet.doPost(AbstractHTTPServlet.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:616)
at
org.apache.cxf.transport.servlet.AbstractHTTPServlet.service(AbstractHTTPServlet.java:197)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:427)
at
org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:832)
at
com.planetj.servlet.filter.compression.CompressingFilter.doFilter(CompressingFilter.java:222)
at
org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:823)
at
org.mypkg.servlet.BaseServletManager$CompressingFilterWrapper.doFilter(BaseServletManager.java:780)
at
org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:823)
at
org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:473)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:567)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1565)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1517)
at org.mortbay.http.HttpServer.service(HttpServer.java:954)
at org.mortbay.http.HttpConnection.service(HttpConnection.java:820)
at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:987)
at org.mortbay.http.HttpConnection.handle(HttpConnection.java:837)
at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:244)
at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:357)
at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:534)
Caused by: javax.xml.bind.JAXBException: class java.util.HashMap nor any of
its super class is known to this context.
at
com.sun.xml.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:247)
at
com.sun.xml.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:262)
at
com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:653)
at
com.sun.xml.bind.v2.runtime.property.SingleMapNodeProperty.serializeBody(SingleMapNodeProperty.java:275)
at
com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:358)
at
com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:696)
at
com.sun.xml.bind.v2.runtime.property.ArrayElementNodeProperty.serializeItem(ArrayElementNodeProperty.java:69)
at
com.sun.xml.bind.v2.runtime.property.ArrayElementProperty.serializeListBody(ArrayElementProperty.java:172)
at
com.sun.xml.bind.v2.runtime.property.ArrayERProperty.serializeBody(ArrayERProperty.java:159)
at
com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:358)
at
com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:696)
at
com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl$1.serializeBody(ElementBeanInfoImpl.java:156)
at
com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl$1.serializeBody(ElementBeanInfoImpl.java:131)
at
com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl.serializeBody(ElementBeanInfoImpl.java:333)
at
com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl.serializeRoot(ElementBeanInfoImpl.java:340)
at
com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl.serializeRoot(ElementBeanInfoImpl.java:76)
at
com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:494)
at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:323)
... 36 more
Caused by: javax.xml.bind.JAXBException: class java.util.HashMap nor any of
its super class is known to this context.
at
com.sun.xml.bind.v2.runtime.JAXBContextImpl.getBeanInfo(JAXBContextImpl.java:588)
at
com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:648)
... 51 more