diff --git a/core/src/main/scala/spark/rdd/CoGroupedRDD.scala b/core/src/main/scala/spark/rdd/CoGroupedRDD.scala
index 9213513e80914fd7ad67df953e80f04ddc1f07da..a6235491cab9657074a6de200d5b4cc3d5321341 100644
--- a/core/src/main/scala/spark/rdd/CoGroupedRDD.scala
+++ b/core/src/main/scala/spark/rdd/CoGroupedRDD.scala
@@ -29,7 +29,7 @@ private[spark] case class NarrowCoGroupSplitDep(
 private[spark] case class ShuffleCoGroupSplitDep(shuffleId: Int) extends CoGroupSplitDep
 
 private[spark]
-class CoGroupPartition(idx: Int, val deps: Seq[CoGroupSplitDep])
+class CoGroupPartition(idx: Int, val deps: Array[CoGroupSplitDep])
   extends Partition with Serializable {
   override val index: Int = idx
   override def hashCode(): Int = idx
@@ -88,7 +88,7 @@ class CoGroupedRDD[K](
           case _ =>
             new NarrowCoGroupSplitDep(rdd, i, rdd.partitions(i))
         }
-      }.toList)
+      }.toArray)
     }
     array
   }
diff --git a/core/src/main/scala/spark/rdd/ShuffledRDD.scala b/core/src/main/scala/spark/rdd/ShuffledRDD.scala
index 51f02409b6a75d689159970e59af52f887fc8626..4e33b7dd5ca844b4dc425b72fd1f09a2893e5e1d 100644
--- a/core/src/main/scala/spark/rdd/ShuffledRDD.scala
+++ b/core/src/main/scala/spark/rdd/ShuffledRDD.scala
@@ -16,7 +16,7 @@ private[spark] class ShuffledRDDPartition(val idx: Int) extends Partition {
  * @tparam V the value class.
  */
 class ShuffledRDD[K, V](
-    prev: RDD[(K, V)],
+    @transient prev: RDD[(K, V)],
     part: Partitioner)
   extends RDD[(K, V)](prev.context, List(new ShuffleDependency(prev, part))) {
 
diff --git a/core/src/main/scala/spark/rdd/SubtractedRDD.scala b/core/src/main/scala/spark/rdd/SubtractedRDD.scala
index 0a025610626779209c575caadbcd2067fb34a232..481e03b349af0d7681ef5d25d6f3ac07bfec69f5 100644
--- a/core/src/main/scala/spark/rdd/SubtractedRDD.scala
+++ b/core/src/main/scala/spark/rdd/SubtractedRDD.scala
@@ -56,7 +56,7 @@ private[spark] class SubtractedRDD[K: ClassManifest, V: ClassManifest, W: ClassM
           case _ =>
             new NarrowCoGroupSplitDep(rdd, i, rdd.partitions(i))
         }
-      }.toList)
+      }.toArray)
     }
     array
   }