diff --git a/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala b/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala
index 19287edbaf166..ae7e7dd7c8d35 100644
--- a/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala
+++ b/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala
@@ -291,6 +291,8 @@ private[spark] class ExternalSorter[K, V, C](
       val it = collection.destructiveSortedWritablePartitionedIterator(comparator)
       while (it.hasNext) {
         val partitionId = it.nextPartition()
+        require(partitionId >= 0 && partitionId < numPartitions,
+          s"partition Id: ${partitionId} should be in the range [0, ${numPartitions})")
         it.writeNext(writer)
         elementsPerPartition(partitionId) += 1
         objectsWritten += 1