diff --git a/library/src/main/java/net/sharewire/googlemapsclustering/ClusterManager.java b/library/src/main/java/net/sharewire/googlemapsclustering/ClusterManager.java
index 83492a5..3b3eea6 100644
--- a/library/src/main/java/net/sharewire/googlemapsclustering/ClusterManager.java
+++ b/library/src/main/java/net/sharewire/googlemapsclustering/ClusterManager.java
@@ -214,8 +214,8 @@ private QuadTreeTask(@NonNull List<T> clusterItems) {
         @Override
         protected Void doInBackground(Void... params) {
             mQuadTree.clear();
-            for (T clusterItem : mClusterItems) {
-                mQuadTree.insert(clusterItem);
+            for (int i = 0; i < mClusterItems.size(); i++) {
+                mQuadTree.insert(mClusterItems.get(i));
             }
             return null;
         }