diff --git a/core/src/main/scala/org/apache/spark/util/BoundedPriorityQueue.scala b/core/src/main/scala/org/apache/spark/util/BoundedPriorityQueue.scala
index 0b51c23f7b2803498e527f56ad07e1e889aa1436..a38329df037a14ae6ec0e4bba7278990a4243480 100644
--- a/core/src/main/scala/org/apache/spark/util/BoundedPriorityQueue.scala
+++ b/core/src/main/scala/org/apache/spark/util/BoundedPriorityQueue.scala
@@ -34,6 +34,8 @@ class BoundedPriorityQueue[A](maxSize: Int)(implicit ord: Ordering[A])
 
   override def iterator: Iterator[A] = underlying.iterator.asScala
 
+  override def size: Int = underlying.size
+
   override def ++=(xs: TraversableOnce[A]): this.type = {
     xs.foreach { this += _ }
     this