diff --git a/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala b/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala
index 5146f12..199640b 100644
--- a/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala
+++ b/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala
@@ -138,7 +138,8 @@ class ReplicaStateMachine(controller: KafkaController) extends Logging {
             case NewReplica =>
               // add this replica to the assigned replicas list for its partition
               val currentAssignedReplicas = controllerContext.partitionReplicaAssignment(topicAndPartition)
-              controllerContext.partitionReplicaAssignment.put(topicAndPartition, currentAssignedReplicas :+ replicaId)
+              if(!currentAssignedReplicas.contains(replicaId))
+                controllerContext.partitionReplicaAssignment.put(topicAndPartition, currentAssignedReplicas :+ replicaId)
               stateChangeLogger.trace("Controller %d epoch %d changed state of replica %d for partition %s to OnlineReplica"
                                         .format(controllerId, controller.epoch, replicaId, topicAndPartition))
             case _ =>