diff --git a/mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala b/mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala
index 84cff9bbf61d1..e03b784a368f7 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala
@@ -289,10 +289,12 @@ private[python] class PythonMLLibAPI extends Serializable {
       data: JavaRDD[Vector],
       isotonic: Boolean): JList[Object] = {
     val isotonicRegressionAlg = new IsotonicRegression().setIsotonic(isotonic)
+    val input = data.rdd.map { x =>
+      (x(0), x(1), x(2))
+    }.persist(StorageLevel.MEMORY_AND_DISK)
     try {
-      val model = isotonicRegressionAlg.run(data.rdd.map(_.toArray).map {
-        x => (x(0), x(1), x(2)) }.persist(StorageLevel.MEMORY_AND_DISK))
-      List(model.boundaries, model.predictions).map(_.asInstanceOf[Object]).asJava
+      val model = isotonicRegressionAlg.run(input)
+      List[AnyRef](model.boundaryVector, model.predictionVector).asJava
     } finally {
       data.rdd.unpersist(blocking = false)
     }
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala b/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala
index 15a0760f5e6c1..be2a00c2dfea4 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala
@@ -28,12 +28,13 @@ import org.json4s._
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods._
 
+import org.apache.spark.SparkContext
 import org.apache.spark.annotation.Experimental
 import org.apache.spark.api.java.{JavaDoubleRDD, JavaRDD}
+import org.apache.spark.mllib.linalg.{Vector, Vectors}
 import org.apache.spark.mllib.util.{Loader, Saveable}
 import org.apache.spark.rdd.RDD
-import org.apache.spark.SparkContext
-import org.apache.spark.sql.{DataFrame, SQLContext}
+import org.apache.spark.sql.SQLContext
 
 /**
  * :: Experimental ::
@@ -140,6 +141,12 @@ class IsotonicRegressionModel (
     }
   }
 
+  /** A convenient method for boundaries called by the Python API. */
+  private[mllib] def boundaryVector: Vector = Vectors.dense(boundaries)
+
+  /** A convenient method for boundaries called by the Python API. */
+  private[mllib] def predictionVector: Vector = Vectors.dense(predictions)
+
   override def save(sc: SparkContext, path: String): Unit = {
     IsotonicRegressionModel.SaveLoadV1_0.save(sc, path, boundaries, predictions, isotonic)
   }
diff --git a/python/pyspark/mllib/regression.py b/python/pyspark/mllib/regression.py
index 8d6e3d85a4341..41bde2ce3e60b 100644
--- a/python/pyspark/mllib/regression.py
+++ b/python/pyspark/mllib/regression.py
@@ -445,17 +445,16 @@ def save(self, sc, path):
     def load(cls, sc, path):
         java_model = sc._jvm.org.apache.spark.mllib.regression.IsotonicRegressionModel.load(
             sc._jsc.sc(), path)
-        py_boundaries = _java2py(sc, java_model.boundaries())
-        py_predictions = _java2py(sc, java_model.predictions())
-        return IsotonicRegressionModel(np.array(py_boundaries),
-                                       np.array(py_predictions), java_model.isotonic)
+        py_boundaries = _java2py(sc, java_model.boundaryVector()).toArray()
+        py_predictions = _java2py(sc, java_model.predictionVector()).toArray()
+        return IsotonicRegressionModel(py_boundaries, py_predictions, java_model.isotonic)
 
 
 class IsotonicRegression(object):
     """
     Run IsotonicRegression algorithm to obtain isotonic regression model.
 
-    :param data:            RDD of data points
+    :param data:            RDD of (label, feature, weight) tuples.
     :param isotonic:        Whether this is isotonic or antitonic.
     """
     @classmethod
@@ -463,7 +462,7 @@ def train(cls, data, isotonic=True):
         """Train a isotonic regression model on the given data."""
         boundaries, predictions = callMLlibFunc("trainIsotonicRegressionModel",
                                                 data.map(_convert_to_vector), bool(isotonic))
-        return IsotonicRegressionModel(np.array(boundaries), np.array(predictions), isotonic)
+        return IsotonicRegressionModel(boundaries.toArray(), predictions.toArray(), isotonic)
 
 
 def _test():