diff --git a/nvflare/lighter/tree_prov.py b/nvflare/lighter/tree_prov.py
index 5c39a0addf..628121d65c 100644
--- a/nvflare/lighter/tree_prov.py
+++ b/nvflare/lighter/tree_prov.py
@@ -67,8 +67,9 @@ class PortManager:
 
     @classmethod
     def get_port(cls):
-        cls.last_port_number += 1
-        return cls.last_port_number
+        num = cls.last_port_number + 1
+        cls.last_port_number = num
+        return num
 
 
 class _Node: