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 689ba9b9bfff8dc9e95ad445c0218515b72874e1..2c237442f4538579b8323f4c68fbbcfd57cefe55 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
@@ -92,7 +92,7 @@ private[spark] class MemoryStore(
   private class OurBlockIdAndSizeType(
       private var blockId: BlockId,
       private var size: Long) extends Ordering[OurBlockIdAndSizeType] {
-    def compare(other: OurBlockIdAndSizeType) = this.size.compare(other.size)
+    def compare(other: OurBlockIdAndSizeType): Int = this.size.compare(other.size)
   }
 
   private val entries = new LinkedHashMap[BlockId, MemoryEntry[_]](32, 0.75f, true)