diff --git a/pyproject.toml b/pyproject.toml
index af38eaa..f6e78eb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,7 +5,7 @@ build-backend = "poetry.core.masonry.api"
 
 [tool.poetry]
 name = "x10-python-trading-starknet"
-version = "2.4.1"
+version = "2.5.0"
 description = "Python client for X10 API"
 authors = ["X10 <tech@ex10.org>"]
 repository = "https://github.com/x10xchange/python_sdk"
diff --git a/x10/models/order.py b/x10/models/order.py
index 4cd02f4..c200169 100644
--- a/x10/models/order.py
+++ b/x10/models/order.py
@@ -10,6 +10,7 @@ class TimeInForce(StrEnum):
     GTT = "GTT"
     IOC = "IOC"
     FOK = "FOK"
+    TOB = "TOB"
 
 
 class OrderSide(StrEnum):
diff --git a/x10/signing/order_object.py b/x10/signing/order_object.py
index db64c23..2693af6 100644
--- a/x10/signing/order_object.py
+++ b/x10/signing/order_object.py
@@ -209,6 +209,9 @@ def validate_tpsl_order():
     if time_in_force == TimeInForce.FOK:
         raise ValidationError("FOK `time_in_force` value is deprecated")
 
+    if time_in_force == TimeInForce.TOB and not post_only:
+        raise ValidationError("`post_only` must be true for TOB `time_in_force`")
+
     if expire_time is None:
         raise ValidationError("`expire_time` must be provided")