diff --git a/ibkr/option_leg.py b/ibkr/option_leg.py
index 4641cb1..885f986 100644
--- a/ibkr/option_leg.py
+++ b/ibkr/option_leg.py
@@ -2,7 +2,7 @@ from dataclasses import dataclass
 from datetime import datetime
 from typing import Literal
 
-@dataclass
+@dataclass(frozen=True)
 class OptionLeg:
     symbol: str
     expiration: datetime