The attached application demonstrates the issue. Deploy, undeploy, heap dump. The application contains a ServletContextListener that creates a static reference to a "LeakMarker" object to simplify finding the leaked ModuleClassLoader. org.xnio.nio.WorkerThread @ 0x7b90fa3b0 XNIO-1 I/O-2 Thread '- contextClassLoader org.jboss.modules.ModuleClassLoader @ 0x7b8224be0 '- module org.jboss.modules.Module @ 0x7b8224b40 '- moduleLoader org.jboss.modules.LocalModuleLoader @ 0x7b82241e0 '- moduleMap org.jboss.modules.UnlockedReadHashMap @ 0x7b8224220 '- table java.util.concurrent.atomic.AtomicReferenceArray @ 0x7b8224270 '- array java.lang. Object [512] @ 0x7b8224280 '- [345] org.jboss.modules.UnlockedReadHashMap$Item[1] @ 0x7b8010000 '- [0] org.jboss.modules.UnlockedReadHashMap$Item @ 0x7b8010018 '- value org.jboss.modules.ModuleLoader$FutureModule @ 0x7b8010030 '- module org.jboss.modules.Module @ 0x7b84c1360 '- moduleClassLoader org.jboss.modules.ModuleClassLoader @ 0x7b84c0f98 '- classes java.util.Vector @ 0x7b84c1078 '- elementData java.lang. Object [20] @ 0x7b9597c20 '- [10] class org.jboss.el.cache.FactoryFinderCache @ 0x7b9597d48 '- CLASS_CACHE java.util.concurrent.ConcurrentHashMap @ 0x7b9597db0 '- table java.util.concurrent.ConcurrentHashMap$Node[16] @ 0x7b9597df0 '- [5] java.util.concurrent.ConcurrentHashMap$Node @ 0x7bf5b6b40 '- key org.jboss.el.cache.FactoryFinderCache$CacheKey @ 0x7bf5b6b60 '- loader org.jboss.modules.ModuleClassLoader @ 0x7bf380c78 '- classes java.util.Vector @ 0x7bf380df8 '- elementData java.lang. Object [10] @ 0x7bf380e18 '- [0] class leak.LeakListener @ 0x7bf388a88 '- LEAK_MARKER leak.LeakMarker @ 0x7bf388af0