diff --git a/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAOptimizer.scala b/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAOptimizer.scala
index 38486e949bbcfae5d1872cff6f6e22b95035bcc5..17c0609800e903a39d338a54dd413728426dcd77 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAOptimizer.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAOptimizer.scala
@@ -438,7 +438,7 @@ final class OnlineLDAOptimizer extends LDAOptimizer {
 
       val stat = BDM.zeros[Double](k, vocabSize)
       var gammaPart = List[BDV[Double]]()
-      nonEmptyDocs.zipWithIndex.foreach { case ((_, termCounts: Vector), idx: Int) =>
+      nonEmptyDocs.foreach { case (_, termCounts: Vector) =>
         val ids: List[Int] = termCounts match {
           case v: DenseVector => (0 until v.size).toList
           case v: SparseVector => v.indices.toList