diff --git a/data_structures/stacks/postfix_evaluation.py b/data_structures/stacks/postfix_evaluation.py
index dea29858d..bac96cdbc 100644
--- a/data_structures/stacks/postfix_evaluation.py
+++ b/data_structures/stacks/postfix_evaluation.py
@@ -74,7 +74,7 @@ def is_operator(data: str) -> bool:
     return data in ["-", "+", "*", "^", "/"]
 
 
-def evaluate(post_fix: list, verbose: bool = False) -> int:
+def evaluate(post_fix: list, verbose: bool = False) -> int | float | str | None:
     """
     Function that evaluates postfix expression using a stack.
     >>> evaluate(["2", "1", "+", "3", "*"])