diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala
index 4992d5db1f57a..cdbd06200c7bd 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala
@@ -50,7 +50,6 @@ private[feature] trait StringIndexerBase extends Params with HasInputCol with Ha
     val outputFields = inputFields :+ attr.toStructField()
     StructType(outputFields)
   }
-
 }
 
 /**
@@ -159,7 +158,7 @@ class StringIndexerModel private[ml] (
    * Note: By default we keep the original columns during this transformation, so the inverse
    * should only be used on new columns such as predicted labels.
    */
-  def invert(inputCol: String, outputCol: String): StringIndexerInverseTransformer = {
+  def invert(inputCol: String, outputCol: String): StringIndexerInverse = {
     val labelsCol: String = $(this.outputCol)
     new StringIndexerInverseTransformer(labelsCol)
       .setInputCol(inputCol)
@@ -174,7 +173,7 @@ class StringIndexerModel private[ml] (
  * so the inverse should only be used on new columns such as predicted labels.
  */
 @Experimental
-class StringIndexerInverseTransformer private[ml] (
+class StringIndexerInverse private[ml] (
   override val uid: String,
   val labelsCol: String) extends Transformer
     with HasInputCol with HasOutputCol {
@@ -210,7 +209,7 @@ class StringIndexerInverseTransformer private[ml] (
     val values = attr.values.get
     val indexer = udf { index: Double =>
       val idx = index.toInt
-      if (0 <= idx && idx <= values.size) {
+      if (0 <= idx && idx < values.size) {
         values(idx)
       } else {
         throw new SparkException(s"Unseen index: $index ??")
@@ -218,7 +217,7 @@ class StringIndexerInverseTransformer private[ml] (
     }
     val outputColName = $(outputCol)
     dataset.select(col("*"),
-      indexer(dataset($(inputCol)).cast(StringType)).as(outputColName))
+      indexer(dataset($(inputCol)).cast(DoubleType)).as(outputColName))
   }
 
   override def copy(extra: ParamMap): StringIndexerInverseTransformer = {