diff --git a/Quadtree.cs b/Quadtree.cs
index 99a7869..db1036a 100644
--- a/Quadtree.cs
+++ b/Quadtree.cs
@@ -47,8 +47,16 @@ namespace Quadtree
         /// </summary>
         private float m_maxObjectRadius;
 
+        /// <summary>
+        /// Stack of vertex indices with their bounding boxes. It is reused for each query.
+        /// </summary>
         private Stack<QuadtreeQuery> _queryStack;
 
+        /// <summary>
+        /// Stack of vertex indices. It is reused for each query.
+        /// </summary>
+        private Stack<int> _vertexStack;
+
         public Quadtree(int maxLeafSize, int maxTreeDepth)
         {
             m_maxLeafSize = maxLeafSize;
@@ -58,6 +66,7 @@ namespace Quadtree
             m_rootBoundingBox = new BoundingBox2(Vector2.Zero, Vector2.Zero);
             m_maxObjectRadius = 0f;
             _queryStack = new Stack<QuadtreeQuery>();
+            _vertexStack = new Stack<int>();
         }
 
         public void Add(IWorldObject obj)
@@ -347,21 +356,19 @@ namespace Quadtree
 
         private void QueryAppendContainedItems(int vertexIndex, BoundingBox2 box, List<IWorldObject> resultList)
         {
-            // TODO: Stack as reused member variable?
-            Stack<int> stack = new Stack<int>();
-            stack.Push(vertexIndex);
+            _vertexStack.Push(vertexIndex);
 
-            while (stack.Count > 0)
+            while (_vertexStack.Count > 0)
             {
-                int current = stack.Pop();
+                int current = _vertexStack.Pop();
                 if (m_vertices[current].ChildCount == -1)
                 {
                     // Branches into all vertices until leaves are found.
                     int childIndex = m_vertices[current].FirstChildIndex;
-                    stack.Push(childIndex++);
-                    stack.Push(childIndex++);
-                    stack.Push(childIndex++);
-                    stack.Push(childIndex);
+                    _vertexStack.Push(childIndex++);
+                    _vertexStack.Push(childIndex++);
+                    _vertexStack.Push(childIndex++);
+                    _vertexStack.Push(childIndex);
                 }
                 else
                 {