diff --git a/core/src/main/scala/org/apache/spark/scheduler/InputFormatInfo.scala b/core/src/main/scala/org/apache/spark/scheduler/InputFormatInfo.scala
index 5555585c8b4cdfe6ff408d87660b6c7b1be533ea..b3f2cb346f7dac34742e7b55320cce639c872478 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/InputFormatInfo.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/InputFormatInfo.scala
@@ -164,8 +164,7 @@ object InputFormatInfo {
 
     PS: I know the wording here is weird, hopefully it makes some sense !
   */
-  def computePreferredLocations(formats: Seq[InputFormatInfo]): HashMap[String, HashSet[SplitInfo]]
-  = {
+  def computePreferredLocations(formats: Seq[InputFormatInfo]): Map[String, Set[SplitInfo]] = {
 
     val nodeToSplit = new HashMap[String, HashSet[SplitInfo]]
     for (inputSplit <- formats) {
@@ -178,6 +177,6 @@ object InputFormatInfo {
       }
     }
 
-    nodeToSplit
+    nodeToSplit.mapValues(_.toSet).toMap
   }
 }