diff --git a/core/src/main/scala/org/apache/spark/storage/memory/MemoryStore.scala b/core/src/main/scala/org/apache/spark/storage/memory/MemoryStore.scala
index 2c237442f4538579b8323f4c68fbbcfd57cefe55..43c79ce8f2b44b84056c8bfbae1d7fefa2379181 100644
--- a/core/src/main/scala/org/apache/spark/storage/memory/MemoryStore.scala
+++ b/core/src/main/scala/org/apache/spark/storage/memory/MemoryStore.scala
@@ -91,7 +91,7 @@ private[spark] class MemoryStore(
 
   private class OurBlockIdAndSizeType(
       private var blockId: BlockId,
-      private var size: Long) extends Ordering[OurBlockIdAndSizeType] {
+      private var size: Long) extends Ordered[OurBlockIdAndSizeType] {
     def compare(other: OurBlockIdAndSizeType): Int = this.size.compare(other.size)
   }