I have a decision table with one CONDITION column. My fact could match multiple rules (rows) of the decision table. With each match, the 'ACTION' cause the fact itself to change. I'm using 'modify' as follows to change my fact: modify ($line) { addItem( new Item("DISCOUNT","25%")); } (essentially I need to add a item to a line when ever the LHS matches). This works fine when I use a DRL. But when I try to use a decsion table, I get 'java.util.ConcurrentModificationException' the second time my fact matches a rule. Does anyone know if we can modify facts from decision tables ? All the examples I've seen so far don't show how decision tables handle updating of facts. Here's the stack trace I get : org.drools.runtime.rule.ConsequenceException: java.util.ConcurrentModificationException at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleEx ception(DefaultConsequenceExceptionHandler.java:23) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:943) at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:885) at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1082) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemo ry.java:682) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemo ry.java:649) at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowle dgeSessionImpl.java:177) at com.sample.DecisionTableTest.main(DecisionTableTest.java:31) Caused by: java.util.ConcurrentModificationException at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372) at java.util.AbstractList$Itr.next(AbstractList.java:343) at com.sample.Line.addPromotion(Line.java:46) at com.lazboy.promotions.Rule_Group_Promotion_14_0.consequence(Rule_Group_P romotion_14_0.java:7) at com.lazboy.promotions.Rule_Group_Promotion_14_0ConsequenceInvoker.evalua te(Rule_Group_Promotion_14_0ConsequenceInvoker.java:22) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:934) ... 6 more I'm using Drools Expert 5.0.1. Thanks Gurvinder