diff --git a/lib/var_stack.py b/lib/var_stack.py
index 0b73b91..3ea3813 100644
--- a/lib/var_stack.py
+++ b/lib/var_stack.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 r"""
 Define the var_stack class.