diff --git a/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleSortDataFormat.java b/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleSortDataFormat.java
index 8f4e3229976dc..1e924d2aec442 100644
--- a/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleSortDataFormat.java
+++ b/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleSortDataFormat.java
@@ -61,10 +61,10 @@ public void copyElement(LongArray src, int srcPos, LongArray dst, int dstPos) {
   public void copyRange(LongArray src, int srcPos, LongArray dst, int dstPos, int length) {
     Platform.copyMemory(
       src.getBaseObject(),
-      src.getBaseOffset() + srcPos * 8,
+      src.getBaseOffset() + srcPos * 8L,
       dst.getBaseObject(),
-      dst.getBaseOffset() + dstPos * 8,
-      length * 8
+      dst.getBaseOffset() + dstPos * 8L,
+      length * 8L
     );
   }
 
diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSortDataFormat.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSortDataFormat.java
index d19b71fbc1bcb..7bda76907f4c3 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSortDataFormat.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSortDataFormat.java
@@ -75,10 +75,10 @@ public void copyElement(LongArray src, int srcPos, LongArray dst, int dstPos) {
   public void copyRange(LongArray src, int srcPos, LongArray dst, int dstPos, int length) {
     Platform.copyMemory(
       src.getBaseObject(),
-      src.getBaseOffset() + srcPos * 16,
+      src.getBaseOffset() + srcPos * 16L,
       dst.getBaseObject(),
-      dst.getBaseOffset() + dstPos * 16,
-      length * 16);
+      dst.getBaseOffset() + dstPos * 16L,
+      length * 16L);
   }
 
   @Override
diff --git a/core/src/test/scala/org/apache/spark/util/collection/ExternalSorterSuite.scala b/core/src/test/scala/org/apache/spark/util/collection/ExternalSorterSuite.scala
index 4dd8e31c27351..699f7fa1f2727 100644
--- a/core/src/test/scala/org/apache/spark/util/collection/ExternalSorterSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/collection/ExternalSorterSuite.scala
@@ -17,12 +17,17 @@
 
 package org.apache.spark.util.collection
 
+import java.util.Comparator
+
 import scala.collection.mutable.ArrayBuffer
 import scala.util.Random
 
 import org.apache.spark._
 import org.apache.spark.memory.MemoryTestingUtils
 import org.apache.spark.serializer.{JavaSerializer, KryoSerializer}
+import org.apache.spark.unsafe.array.LongArray
+import org.apache.spark.unsafe.memory.MemoryBlock
+import org.apache.spark.util.collection.unsafe.sort.{PrefixComparators, RecordPointerAndKeyPrefix, UnsafeSortDataFormat}
 
 class ExternalSorterSuite extends SparkFunSuite with LocalSparkContext {
   import TestUtils.{assertNotSpilled, assertSpilled}
@@ -93,6 +98,25 @@ class ExternalSorterSuite extends SparkFunSuite with LocalSparkContext {
   testWithMultipleSer("sort without breaking sorting contracts", loadDefaults = true)(
     sortWithoutBreakingSortingContracts)
 
+  // This test is ignored by default as it requires a fairly large heap size (16GB)
+  ignore("sort without breaking timsort contracts for large arrays") {
+    val size = 300000000
+    // To manifest the bug observed in SPARK-8428 and SPARK-13850, we explicitly use an array of
+    // the form [150000000, 150000001, 150000002, ...., 300000000, 0, 1, 2, ..., 149999999]
+    // that can trigger copyRange() in TimSort.mergeLo() or TimSort.mergeHi()
+    val ref = Array.tabulate[Long](size) { i => if (i < size / 2) size / 2 + i else i }
+    val buf = new LongArray(MemoryBlock.fromLongArray(ref))
+
+    new Sorter(UnsafeSortDataFormat.INSTANCE).sort(
+      buf, 0, size, new Comparator[RecordPointerAndKeyPrefix] {
+        override def compare(
+            r1: RecordPointerAndKeyPrefix,
+            r2: RecordPointerAndKeyPrefix): Int = {
+          PrefixComparators.LONG.compare(r1.keyPrefix, r2.keyPrefix)
+        }
+      })
+  }
+
   test("spilling with hash collisions") {
     val size = 1000
     val conf = createSparkConf(loadDefaults = true, kryo = false)