That is the very same issue I encounter today, deploying an .aar Axis archive into an embedded tomcat. Hibernate classes are found by the AppClassLoader, .aar is loaded by ParallelWebappClassLoader. This worked with Hibernate < 4, because it always used the contextClassLoader. The behavior was implicitly changed in 726305f33ef11f2f3b6b2a08352da3cc392df5da and c2330c29f651d370ca0b8d205a79af7f741f75ec, and no one bothered to ask for a test that could have revealed the now faulty behavior.