Hi all, I am upgrading an application from 5.3.0.Final to 5.4.0.Final and I am getting the following exception: Exception executing consequence for rule "ruleThatFails" in indexingproblem.remove.me.anditworks: java.lang.UnsupportedOperationException at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1287) at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1212) at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1446) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:710) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:674) at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:230) at com.mycompany.app.IndexingProblemMain.main(IndexingProblemMain.java:36) Caused by: java.lang.UnsupportedOperationException at org.drools.reteoo.BaseLeftTuple.getPrevious(BaseLeftTuple.java:480) at org.drools.core.util.index.LeftTupleList.remove(LeftTupleList.java:114) at org.drools.core.util.index.LeftTupleList.removeAdd(LeftTupleList.java:68) at org.drools.reteoo.JoinNode.modifyLeftTuple(JoinNode.java:310) at org.drools.reteoo.LeftTupleSource.doModifyLeftTuple(LeftTupleSource.java:304) at org.drools.reteoo.LeftTupleSource.modifyLeftTuple(LeftTupleSource.java:278) at org.drools.reteoo.JoinNode.modifyLeftTuple(JoinNode.java:437) at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateModifyLeftTuple(SingleLeftTupleSinkAdapter.java:205) at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateModifyObject(SingleLeftTupleSinkAdapter.java:235) at org.drools.reteoo.LeftInputAdapterNode.modifyObject(LeftInputAdapterNode.java:170) at org.drools.reteoo.SingleObjectSinkAdapter.propagateModifyObject(SingleObjectSinkAdapter.java:68) at org.drools.reteoo.AlphaNode.modifyObject(AlphaNode.java:157) at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateModifyObject(CompositeObjectSinkAdapter.java:507) at org.drools.reteoo.CompositeObjectSinkAdapter.propagateModifyObject(CompositeObjectSinkAdapter.java:421) at org.drools.reteoo.ObjectTypeNode.modifyObject(ObjectTypeNode.java:314) at org.drools.reteoo.EntryPointNode.modifyObject(EntryPointNode.java:265) at org.drools.common.NamedEntryPoint.update(NamedEntryPoint.java:483) at org.drools.common.NamedEntryPoint.update(NamedEntryPoint.java:383) at org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:337) at indexingproblem.remove.me.anditworks.Rule_ruleThatFails_b159773c7b1a41a2a93044d2816b96ca.defaultConsequence(Rule_ruleThatFails_b159773c7b1a41a2a93044d2816b96ca.java:9) at indexingproblem.remove.me.anditworks.Rule_ruleThatFails_b159773c7b1a41a2a93044d2816b96caDefaultConsequenceInvokerGenerated.evaluate(Unknown Source) at indexingproblem.remove.me.anditworks.Rule_ruleThatFails_b159773c7b1a41a2a93044d2816b96caDefaultConsequenceInvoker.evaluate(Unknown Source) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1277) ... 6 more I have tried to create a minimal test case that recreates this issue, here it is: package indexingproblem.remove.me.anditworks; declare Criteria processed : boolean end declare CheeseCriteria extends Criteria end rule setUp salience 10000 when then insert(new CheeseCriteria()); end rule aaa when CheeseCriteria( ) then end rule bbb when CheeseCriteria( ) then end rule ccc when CheeseCriteria( ) then end rule eeeFalse when Criteria( processed == false ) then end declare Filter end rule fffTrue when Criteria( processed == true ) Filter( ) then end rule ruleThatFails when $criteria : Criteria( processed == false ) then modify($criteria) { setProcessed(true) } end I've tried to run it on 5.5.0-SNAPSHOT, but I got the same result. Note that if you change the rule package to be "package indexingproblem" the exception is not thrown. The code for building the KnowledgeBase is standard, I haven't used any additional options. No fact is inserted only one fireAllRules call. Please let me know if I should create a new JIRA ticket for this or if I am doing something wrong. Thanking you in advance. Best regards, Michal