The NullPointerException reported by Tibor is not caused by a concurrency issue, but by the LRU cache that we introduced to workaround this other problem https://bugzilla.redhat.com/show_bug.cgi?id=1273368 That cache by default has a max size of 100 items https://github.com/droolsjbpm/drools/blob/master/drools-compiler/src/main/java/org/drools/compiler/kie/builder/impl/KieRepositoryImpl.java#L257 and increasing this size makes the NPE to disappear.