diff --git a/eitprocessing/datahandling/eitdata.py b/eitprocessing/datahandling/eitdata.py
index b1e52da64..b7108fc65 100644
--- a/eitprocessing/datahandling/eitdata.py
+++ b/eitprocessing/datahandling/eitdata.py
@@ -4,15 +4,18 @@
 from dataclasses import dataclass, field
 from enum import auto
 from pathlib import Path
-from typing import TypeVar
+from typing import TYPE_CHECKING, TypeVar
 
 import numpy as np
 from strenum import LowercaseStrEnum
-from typing_extensions import Self
 
 from eitprocessing.datahandling import DataContainer
 from eitprocessing.datahandling.mixins.slicing import SelectByTime
 
+if TYPE_CHECKING:
+    from typing_extensions import Self
+
+
 T = TypeVar("T", bound="EITData")
 
 
diff --git a/pyproject.toml b/pyproject.toml
index e278ecdac..d2883d9cd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -36,6 +36,7 @@ dependencies = [
     "tqdm >= 4.65.0",
     "strenum >= 0.4.10",
     "anytree >= 2.12.1 ",
+    "typing_extensions",
 ]
 
 [project.optional-dependencies]