diff --git a/Tree/ValidateBinarySearchTree.swift b/Tree/ValidateBinarySearchTree.swift
index 6d3cc937..dd9afe06 100644
--- a/Tree/ValidateBinarySearchTree.swift
+++ b/Tree/ValidateBinarySearchTree.swift
@@ -21,15 +21,15 @@ class ValidateBinarySearchTree {
         return _helper(root, nil, nil)
     }
     
-    private func _helper(node: TreeNode?, _ min: Int?, _ max: Int?) -> Bool {
+    private func _helper(_ node: TreeNode?, _ min: Int?, _ max: Int?) -> Bool {
         guard let node = node else {
             return true
         }
         
-        if let min = min, root.val <= min {
+        if let min = min, node.val <= min {
             return false
         }
-        if let max = max, root.val >= max {
+        if let max = max, node.val >= max {
             return false
         }