diff --git a/mllib/src/main/scala/org/apache/spark/mllib/fpm/LocalPrefixSpan.scala b/mllib/src/main/scala/org/apache/spark/mllib/fpm/LocalPrefixSpan.scala
index 53760645a53af..6a418dcc6fe82 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/fpm/LocalPrefixSpan.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/fpm/LocalPrefixSpan.scala
@@ -48,19 +48,19 @@ private[fpm] object LocalPrefixSpan extends Logging with Serializable {
     if (database.isEmpty) return Iterator.empty
 
     val frequentItemAndCounts = getFreqItemAndCounts(minCount, database)
-    val frequentItems = frequentItemAndCounts.map(_._1)
+    val frequentItems = frequentItemAndCounts.map(_._1).toSet
     val frequentPatternAndCounts = frequentItemAndCounts
       .map { case (item, count) => ((item :: prefix).reverse.toArray, count) }
 
     val filteredProjectedDatabase = database.map(x => x.filter(frequentItems.contains(_)))
 
     if (prefix.length + 1 < maxPatternLength) {
-      frequentPatternAndCounts ++ frequentItems.flatMap { item =>
+      frequentPatternAndCounts.iterator ++ frequentItems.flatMap { item =>
         val nextProjected = project(filteredProjectedDatabase, item)
         run(minCount, maxPatternLength, item :: prefix, nextProjected)
       }
     } else {
-      frequentPatternAndCounts
+      frequentPatternAndCounts.iterator
     }
   }
 
@@ -93,12 +93,11 @@ private[fpm] object LocalPrefixSpan extends Logging with Serializable {
    */
   private def getFreqItemAndCounts(
       minCount: Long,
-      database: Iterable[Array[Int]]): Iterator[(Int, Long)] = {
+      database: Iterable[Array[Int]]): Iterable[(Int, Long)] = {
     database.flatMap(_.distinct)
       .foldRight(Map[Int, Long]().withDefaultValue(0L)) { case (item, ctr) =>
         ctr + (item -> (ctr(item) + 1))
       }
       .filter(_._2 >= minCount)
-      .iterator
   }
 }