diff --git a/core/src/main/scala/org/apache/spark/network/cm/CMBlockTransferService.scala b/core/src/main/scala/org/apache/spark/network/cm/CMBlockTransferService.scala
index 86d6396dfdc2b..227d73c77075c 100644
--- a/core/src/main/scala/org/apache/spark/network/cm/CMBlockTransferService.scala
+++ b/core/src/main/scala/org/apache/spark/network/cm/CMBlockTransferService.scala
@@ -41,12 +41,18 @@ final class CMBlockTransferService(conf: SparkConf, securityManager: SecurityMan
   /**
    * Port number the service is listening on, available only after [[init]] is invoked.
    */
-  override def port: Int = cm.id.port
+  override def port: Int = {
+    checkInit()
+    cm.id.port
+  }
 
   /**
    * Host name the service is listening on, available only after [[init]] is invoked.
    */
-  override def hostName: String = cm.id.host
+  override def hostName: String = {
+    checkInit()
+    cm.id.host
+  }
 
   /**
    * Initialize the transfer service by giving it the BlockDataManager that can be used to fetch
@@ -76,6 +82,7 @@ final class CMBlockTransferService(conf: SparkConf, securityManager: SecurityMan
       port: Int,
       blockIds: Seq[String],
       listener: BlockFetchingListener): Unit = {
+    checkInit()
 
     val cmId = new ConnectionManagerId(hostName, port)
     val blockMessageArray = new BlockMessageArray(blockIds.map { blockId =>
@@ -118,6 +125,7 @@ final class CMBlockTransferService(conf: SparkConf, securityManager: SecurityMan
       blockId: String,
       blockData: ManagedBuffer,
       level: StorageLevel) {
+    checkInit()
     val msg = PutBlock(BlockId(blockId), blockData.byteBuffer(), level)
     val blockMessageArray = new BlockMessageArray(BlockMessage.fromPutBlock(msg))
     val remoteCmId = new ConnectionManagerId(hostName, port)
@@ -127,6 +135,10 @@ final class CMBlockTransferService(conf: SparkConf, securityManager: SecurityMan
       Duration.Inf)
   }
 
+  private def checkInit(): Unit = if (cm == null) {
+    throw new IllegalStateException(getClass.getName + " has not been initialized")
+  }
+
   private def onBlockMessageReceive(msg: Message, id: ConnectionManagerId): Option[Message] = {
     logDebug("Handling message " + msg)
     msg match {