diff --git a/core/src/main/scala/org/apache/spark/network/BlockTransferService.scala b/core/src/main/scala/org/apache/spark/network/BlockTransferService.scala
index 2a0a1a0bc0a14..d3ed683c7e880 100644
--- a/core/src/main/scala/org/apache/spark/network/BlockTransferService.scala
+++ b/core/src/main/scala/org/apache/spark/network/BlockTransferService.scala
@@ -94,6 +94,7 @@ abstract class BlockTransferService extends Closeable {
         lock.synchronized {
           val ret = ByteBuffer.allocate(data.size.toInt)
           ret.put(data.nioByteBuffer())
+          ret.flip()
           result = Left(new NioManagedBuffer(ret))
           lock.notify()
         }