You can reproduce the issue with this configuration: <route> <from uri= "direct:multicastParallelAggregate" /> <multicast parallelProcessing= "true" parallelAggregate= "true" strategyRef= "parallelAggregate" > <to uri= "direct:a" /> <to uri= "direct:b" /> </multicast> </route> <route> <from uri= "direct:a" /> <setBody> <constant> A </constant> </setBody> </route> <route> <from uri= "direct:b" /> <setBody> <constant> B </constant> </setBody> </route> <bean id= "parallelAggregate" class= "org.jboss.camel.ParallelAggregate" /> public class ParallelAggregate implements AggregationStrategy { private static boolean invoked; private static boolean calledInParallel; public static boolean isCalledInParallel() { return calledInParallel; } public static void reset() { invoked = calledInParallel = false ; } @Override public Exchange aggregate(Exchange oldExchange, Exchange newExchange) { System .out.println( "A:" + new Date().toString()); synchronized ( this ) { if (!invoked) { invoked = true ; } else { calledInParallel = true ; } } System .out.println( "B:" + new Date().toString()); // Simulate processing, another thread should access aggregator try { Thread .sleep(5000); } catch (InterruptedException e) { throw new RuntimeException(e); } // or like this // long t = new Date().getTime() + 10000; // while (t > new Date().getTime()) { // } System .out.println( "C:" + new Date().toString()); invoked = false ; if (oldExchange == null ) { return newExchange; } oldExchange.getIn().setBody( this .getClass().getName()); return oldExchange; } }