diff --git a/core/src/main/scala/kafka/server/ReplicaManager.scala b/core/src/main/scala/kafka/server/ReplicaManager.scala
index 9d41e82..d885ba1 100644
--- a/core/src/main/scala/kafka/server/ReplicaManager.scala
+++ b/core/src/main/scala/kafka/server/ReplicaManager.scala
@@ -282,9 +282,11 @@ class ReplicaManager(val config: KafkaConfig,
 
   private def maybeShrinkIsr(): Unit = {
     trace("Evaluating ISR list of partitions to see which replicas can be removed from the ISR")
+    var curLeaderPartitions: List[Partition] = null
     leaderPartitionsLock synchronized {
-      leaderPartitions.foreach(partition => partition.maybeShrinkIsr(config.replicaLagTimeMaxMs, config.replicaLagMaxMessages))
+      curLeaderPartitions = leaderPartitions.toList
     }
+    curLeaderPartitions.foreach(partition => partition.maybeShrinkIsr(config.replicaLagTimeMaxMs, config.replicaLagMaxMessages))
   }
 
   def recordFollowerPosition(topic: String, partitionId: Int, replicaId: Int, offset: Long) = {