diff --git a/src/ifc4d/ifc4d/common.py b/src/ifc4d/ifc4d/common.py
index 896f604a61..e433ba9363 100644
--- a/src/ifc4d/ifc4d/common.py
+++ b/src/ifc4d/ifc4d/common.py
@@ -3,7 +3,8 @@ import ifcopenshell
 import ifcopenshell.api
 import ifcopenshell.util.date
 from datetime import datetime, timedelta, date
-from typing import Union, Any, TypedDict, NotRequired
+from typing import Union, Any, TypedDict
+from typing_extensions import NotRequired
 
 
 class WorkSlot(TypedDict):
diff --git a/src/ifc4d/pyproject.toml b/src/ifc4d/pyproject.toml
index 6673061633..6bb2cc9f22 100644
--- a/src/ifc4d/pyproject.toml
+++ b/src/ifc4d/pyproject.toml
@@ -17,6 +17,7 @@ classifiers = [
 ]
 dependencies = [
     "ifcopenshell",
+    "typing-extensions",
 ]
 
 [project.urls]
diff --git a/src/ifcclash/ifcclash/ifcclash.py b/src/ifcclash/ifcclash/ifcclash.py
index 54e4dc0129..10beff94fb 100644
--- a/src/ifcclash/ifcclash/ifcclash.py
+++ b/src/ifcclash/ifcclash/ifcclash.py
@@ -28,7 +28,8 @@ import ifcopenshell
 import ifcopenshell.geom
 import ifcopenshell.util.selector
 from logging import Logger
-from typing import Optional, Literal, TypedDict, NotRequired
+from typing import Literal, TypedDict
+from typing_extensions import NotRequired
 
 
 class ClashSource(TypedDict):